DateTime.Now.ToString("MM/dd/yyyy") 05/29/2015
DateTime.Now.ToString("dddd, dd MMMM yyyy") Friday, 29 May 2015
DateTime.Now.ToString("dddd, dd MMMM yyyy") Friday, 29 May 2015 05:50
DateTime.Now.ToString("dddd, dd MMMM yyyy") Friday, 29 May 2015 05:50 AM
DateTime.Now.ToString("dddd, dd MMMM yyyy") Friday, 29 May 2015 5:50
DateTime.Now.ToString("dddd, dd MMMM yyyy") Friday, 29 May 2015 5:50 AM
DateTime.Now.ToString("dddd, dd MMMM yyyy HH:mm:ss")    Friday, 29 May 2015 05:50:06
DateTime.Now.ToString("MM/dd/yyyy HH:mm")   05/29/2015 05:50
DateTime.Now.ToString("MM/dd/yyyy hh:mm tt")    05/29/2015 05:50 AM
DateTime.Now.ToString("MM/dd/yyyy H:mm")    05/29/2015 5:50
DateTime.Now.ToString("MM/dd/yyyy h:mm tt") 05/29/2015 5:50 AM
DateTime.Now.ToString("MM/dd/yyyy HH:mm:ss")    05/29/2015 05:50:06
DateTime.Now.ToString("MMMM dd")    May 29
DateTime.Now.ToString("yyyy’-‘MM’-‘dd’T’HH’:’mm’:’ss.fffffffK") 2015-05-16T05:50:06.7199222-04:00
DateTime.Now.ToString("ddd, dd MMM yyy HH’:’mm’:’ss ‘GMT’") Fri, 16 May 2015 05:50:06 GMT
DateTime.Now.ToString("yyyy’-‘MM’-‘dd’T’HH’:’mm’:’ss")  2015-05-16T05:50:06
DateTime.Now.ToString("HH:mm")  05:50
DateTime.Now.ToString("hh:mm tt")   05:50 AM
DateTime.Now.ToString("H:mm")   5:50
DateTime.Now.ToString("h:mm tt")    5:50 AM
DateTime.Now.ToString("HH:mm:ss")   05:50:06
DateTime.Now.ToString("yyyy MMMM")  2015 May

如果您使用ReSharper，请使用':'获得帮助(见图)

DateTime.Now.ToString("yyyyMMddHHmmss"); // case sensitive

一个简单的方法，完全控制'从类型'和'到类型'，只需要记住这个代码为未来的类型转换

DateTime.ParseExact(InputDate, "dd/MM/yyyy", CultureInfo.InvariantCulture).ToString("yyyy/MM/dd"));

在.Net Standard 2中，你可以像下面这样格式化DateTime:

DateTime dt = DateTime.Now;
CultureInfo iv = CultureInfo.InvariantCulture;

// Default formats
// D - long date           Tuesday, 24 April 2018
// d - short date          04/24/2018
// F - full date long      Tuesday, 24 April 2018 06:30:00
// f - full date short     Tuesday, 24 April 2018 06:30
// G - general long        04/24/2018 06:30:00
// g - general short       04/24/2018 06:30
// U - universal full      Tuesday, 24 April 2018 06:30:00
// u - universal sortable  2018-04-24 06:30:00
// s - sortable            2018-04-24T06:30:00
// T - long time           06:30:00
// t - short time          06:30
// O - ISO 8601            2018-04-24T06:30:00.0000000
// R - RFC 1123            Tue, 24 Apr 2018 06:30:00 GMT           
// M - month               April 24
// Y - year month          2018 April
Console.WriteLine(dt.ToString("D", iv));

// Custom formats
// M/d/yy                  4/8/18
// MM/dd/yyyy              04/08/2018
// yy-MM-dd                08-04-18
// yy-MMM-dd ddd           08-Apr-18 Sun
// yyyy-M-d dddd           2018-4-8 Sunday
// yyyy MMMM dd            2018 April 08      
// h:mm:ss tt zzz          4:03:05 PM -03
// HH:m:s tt zzz           16:03:05 -03:00
// hh:mm:ss t z            04:03:05 P -03
// HH:mm:ss tt zz          16:03:05 PM -03      
Console.WriteLine(dt.ToString("M/d/yy", iv));

你可以使用自定义格式字符串:

DateTime d = DateTime.Now;
string dateString = d.ToString("yyyyMMddHHmmss");

如果你不想要24小时的时间，就用“hh”代替“hh”。