在日期/时间格式字符串 / 字符表示无论格式提供的日期分隔符是。既然你不提供格式提供 Thread.CurrentCulture 被使用，并在你的情况下，当前文化使用。作为日期分隔符。

如果您想使用的文字的斜线，将它放在单引号内：

 则DateTime.ToString（日日'/'MM'/'YYYY）;
 

另外，你可以在那里的日期分隔符是 / 指定格式提供商

 则DateTime.ToString（DD / MM / YYYY，CultureInfo.InvariantCulture）;
 

以上全部是记录在MSDN上 。

见一个活生生的例子的区别

I have also tried shielding the '/' symbol in the formatting string, but it didn't quite work. My final goal is to get the date with the '/' symbols as separators. I guess I can use DateTime.ToString("dd/MM/yyyy").Replace('.', '/'), but that feels a bit excessive.

The / character in date/time format strings stands for "whatever the date separator of the format provider is". Since you do not supply a format provider Thread.CurrentCulture is used, and in your case the current culture uses . as the date separator.

If you want to use a literal slash, place it inside single quotes:

dateTime.ToString("dd'/'MM'/'yyyy");

Alternatively, you could specify a format provider where the date separator is /:

dateTime.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);

All of the above is documented on MSDN.

See the difference in a live example.