//Unicode转化为汉字:

+(NSString *)replaceUnicode:(NSString*)unicodeStr{
    NSString *tempStr1=[unicodeStr stringByReplacingOccurrencesOfString:@"\\u"withString:@"\\U"];
    NSString *tempStr2=[tempStr1 stringByReplacingOccurrencesOfString:@"\""withString:@"\\\""];
NSString *tempStr3=[[@"\"" stringByAppendingString:tempStr2]stringByAppendingString:@"\""];
NSData *tempData=[tempStr3 dataUsingEncoding:NSUTF8StringEncoding];
NSString* returnStr =[NSPropertyListSerialization propertyListFromData:tempData
                                                     mutabilityOption:NSPropertyListImmutable
                                                               format:NULL
                                                     errorDescription:NULL];

return [returnStr stringByReplacingOccurrencesOfString:@"\\r\\n"withString:@"\n"];

}

//中文转unicode

- (NSString *) utf8ToUnicode:(NSString *)string{

NSUInteger length = [string length];
NSMutableString *str = [NSMutableString stringWithCapacity:0];
for (int i = 0;i < length; i++){
    NSMutableString *s = [NSMutableString stringWithCapacity:0];
    unichar _char = [string characterAtIndex:i];
    // 判断是否为英文和数字
    if (_char <= '9' && _char >='0'){
        [s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i,1)]];
    }else if(_char >='a' && _char <= 'z'){
        [s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i,1)]];
    }else if(_char >='A' && _char <= 'Z')
    {
        [s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i,1)]];
    }else{
        // 中文和字符
        [s appendFormat:@"\\u%x",[string characterAtIndex:i]];
        // 不足位数补0 否则解码不成功
        if(s.length == 4) {
            [s insertString:@"00" atIndex:2];
        } else if (s.length == 5) {
            [s insertString:@"0" atIndex:2];
        }
    }
    [str appendFormat:@"%@", s];
}
return str;

}

补充一下swift版本

/// unicode转中文
///
/// - Parameter unicodeStr: str
/// - Returns:
class func replaceUnicode(unicodeStr: String) -> String {
    let tempStr1 = unicodeStr.replacingOccurrences(of: "\\u", with: "\\U")
    let tempStr2 = tempStr1.replacingOccurrences(of: "\"", with: "\\\"")
    let tempStr3 = "\"".appending(tempStr2).appending("\"")
    let tempData = tempStr3.data(using: String.Encoding.utf8)
    var returnStr:String = ""
    do {
        returnStr = try PropertyListSerialization.propertyList(from: tempData!, options: [.mutableContainers], format: nil) as! String
    } catch {
        print(error)
    }
    return returnStr.replacingOccurrences(of: "\\r\\n", with: "\n")
}     

/// 中文转unicode （utf8）
///
/// - Parameter string: str
/// - Returns:unicode
class func utf8ToUnicode(string: String) -> String {

    let dataEncode = string.data(using: String.Encoding.nonLossyASCII)
    let unicodeStr = String(data: dataEncode!, encoding: String.Encoding.utf8)
    return unicodeStr!
}