找了几天，终于找到一个简单一点的办法，虽然公式有点复杂，让人看不懂，但是效果很好，月份不一样也可以。

I was able to find a product that I used to resolve the "delta" = the difference between dates.

 The link is listed:  http://www.bizsupportonline.net/infopath2007/calculate-date-difference-infopath-rules-formulas.htm

 Calculate the difference between two date picker controls in InfoPath using rules and formulas - no code!

by S.Y.M. Wong-A-Ton | Applies to: InfoPath 2007

Use rules, conditions, and the number(), floor(), and substring() functions in formulas to calculate the difference between two date picker controls in InfoPath.

Use rules, conditions, and the number(), floor(), and substring() functions in formulas to calculate the difference between two date picker controls in InfoPath.

 

Problem

You have a form template with two InfoPath date picker controls and you would like to calculate the difference between the two date picker controls without writing code.

Solution

Use rules, conditions, and the number(), floor(), and substring() functions in formulas to calculate the difference between two date picker controls in InfoPath.

Discussion

You can accomplish this functionality as follows:

1. Design an InfoPath form template as shown in figure 1 with two Date Picker controls named startDate and endDate, and one Text Box control named difference.
   
   Figure 1. InfoPath form template in Design mode.
   
   The Main data source of the InfoPath form template should resemble the following figure:
   
   
   Figure 2. The Main data source of the InfoPath form template.
2. Add the following Rule to the startDate field:
   Action: Set a field's value
   Field: difference
   Value: (number(substring(../my:endDate, 9, 2)) + floor((153 * (number(substring(../my:endDate, 6, 2)) + 12 * (floor((14 - number(substring(../my:endDate, 6, 2))) div 12)) - 3) + 2) div 5) + (number(substring(../my:endDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:endDate, 6, 2))) div 12))) * 365 + floor((number(substring(../my:endDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:endDate, 6, 2))) div 12))) div 4) - floor((number(substring(../my:endDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:endDate, 6, 2))) div 12))) div 100) + floor((number(substring(../my:endDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:endDate, 6, 2))) div 12))) div 400) - 32045) - (number(substring(., 9, 2)) + floor((153 * (number(substring(., 6, 2)) + 12 * (floor((14 - number(substring(., 6, 2))) div 12)) - 3) + 2) div 5) + (number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) * 365 + floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 4) - floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 100) + floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 400) - 32045) with the following Conditions on the Rule:
   startDate is not blank and
   endDate is not blank
3. Add a second Rule to the startDate field with the following settings:
   Action: Set a field's value
   Field: difference
   Value: 0
   
   with the following Conditions on the Rule:
   startDate is blank or
   endDate is blank
4. Add the following Rule to the endDate field:
   Action: Set a field's value
   Field: difference
   Value: (number(substring(., 9, 2)) + floor((153 * (number(substring(., 6, 2)) + 12 * (floor((14 - number(substring(., 6, 2))) div 12)) - 3) + 2) div 5) + (number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) * 365 + floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 4) - floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 100) + floor((number(substring(., 1, 4)) + 4800 - (floor((14 - number(substring(., 6, 2))) div 12))) div 400) - 32045) - (number(substring(../my:startDate, 9, 2)) + floor((153 * (number(substring(../my:startDate, 6, 2)) + 12 * (floor((14 - number(substring(../my:startDate, 6, 2))) div 12)) - 3) + 2) div 5) + (number(substring(../my:startDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:startDate, 6, 2))) div 12))) * 365 + floor((number(substring(../my:startDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:startDate, 6, 2))) div 12))) div 4) - floor((number(substring(../my:startDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:startDate, 6, 2))) div 12))) div 100) + floor((number(substring(../my:startDate, 1, 4)) + 4800 - (floor((14 - number(substring(../my:startDate, 6, 2))) div 12))) div 400) - 32045) with the following Conditions on the Rule:
   startDate is not blank and
   endDate is not blank
5. Add a second Rule to the endDate field with the following settings:
   Action: Set a field's value
   Field: difference
   Value: 0
   
   with the following Conditions on the Rule:
   startDate is blank or
   endDate is blank
6. Add the following Rule to the difference field:
   Action: Set a field's value
   Field: .
   Value: 0
   
   with the following Condition on the Rule:
   difference does not match pattern Custom Pattern: -{0,1}\d+

You should now have a fully functional InfoPath form that will calculate the difference between the dates soon after you have entered valid dates. This solution also works for InfoPath 2003 form templates and InfoPath 2007 browser-enabled form templates.