string str = String.Format("{0:000000000}", 584);          // "000000584"

看到这里:

http://www.csharp-examples.net/string-format-int [ ^ ]

See here:

http://www.csharp-examples.net/string-format-int[^]

string s = 584.ToString().PadLeft(9, '0');

请参见此处 [ ^ ].