文题算是解决了，把特殊字符替换一下：
-(NSString *)JSONString:(NSString
*)aString {
NSMutableString *s =
[NSMutableString
stringWithString:aString];
//[s
replaceOccurrencesOfString:@"\"" withString:@"\\\""
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
//[s
replaceOccurrencesOfString:@"/" withString:@"\\/"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
[s
replaceOccurrencesOfString:@"\n" withString:@"\\n"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
[s
replaceOccurrencesOfString:@"\b" withString:@"\\b"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
[s
replaceOccurrencesOfString:@"\f" withString:@"\\f"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
[s
replaceOccurrencesOfString:@"\r" withString:@"\\r"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
[s
replaceOccurrencesOfString:@"\t" withString:@"\\t"
options:NSCaseInsensitiveSearch range:NSMakeRange(0, [s
length])];
return [NSString
stringWithString:s];
}