、百度一下log4dll下载

、webconfig 里的<configSetions>节点中添加 <section name="log4net" type="System.Configuration.IgnoreSectionHandler" /> 

、增加节点内容如下：

<log4net>

    <appender name="LogFileAppender" type="log4net.Appender.RollingFileAppender">

      <param name="File" value="Log//" />

      <param name="AppendToFile" value="true" />

      <param name="MaxSizeRollBackups" value="" />

      <param name="StaticLogFileName" value="false" />

      <param name="DatePattern" value="yyyy-MM-dd&quot;.log&quot;" />

      <param name="RollingStyle" value="Date" />

      <layout type="log4net.Layout.PatternLayout">

        <param name="ConversionPattern" value="%d 系统异常: %m%n%n" />

      </layout>

    </appender>

    <root>

      <level value="All" />

      <appender-ref ref="LogFileAppender" />

    </root>

  </log4net>

、在引用log4类库、项目中里的AssemblyInfo类中添加日志监视

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Web.config", Watch = true)]

、测试日志代码

 ILog log = log4net.LogManager.GetLogger("LogFileAppender");

               log.Error(ex);