DELPHI code:
unit test1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, StdCtrls, ExtCtrls;

type
 TForm1 = class(TForm)
   Button1: TButton;
   Memo1: TMemo;
   RadioGroup1: TRadioGroup;
   Label1: TLabel;
   procedure Button1Click(Sender: TObject);
   procedure FormShow(Sender: TObject);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}
//procedure DrawToCanvas(Cav: Tcanvas;x,y:integer);Stdcall;external
'KwBarDll.dll';
procedure Epson_Text8d(M:Smallint;F:byte;S:string);stdcall; external
'Epson.dll';
procedure Epson_Text(M:Smallint;F:byte;S:string);stdcall;external
'Epson.dll';
procedure EpsonPrnLn(S:string);stdcall;external 'Epson.dll';
function  GetDefaultPrinter:string;stdcall;external 'Epson.dll';
procedure TForm1.Button1Click(Sender: TObject);
var i:integer;
begin
for i:=0 to Memo1.Lines.Count-1 do
begin
if RadioGroup1.ItemIndex=0 then
  Epson_Text8d(14,0,Memo1.Lines[i]);
if RadioGroup1.ItemIndex=1 then
  Epson_Text(18,0,Memo1.Lines[i]);// print procedure
if RadioGroup1.ItemIndex=2 then
  EpsonPrnLn(Memo1.Lines[i]);
end;
end;

procedure TForm1.FormShow(Sender: TObject);
begin
Label1.Caption:='printer's name£º'+GetDefaultPrinter;
end;

end.

It can print Chinese character,but my C# code:

[DllImport("Epson.dll", EntryPoint = "Epson_Text", CallingConvention =
CallingConvention.StdCall, CharSet = CharSet.Unicode, SetLastError = true,
ExactSpelling = true)]
public static extern void Epson_Text(Int16 M, byte F, string S);
........
string st = "ÖÐÎÄÊDz»ÊDZàÂëÓÐʲôҪÇó";
Epson_Text(18, 0, st);

It can't work.
Anyone has suggest for me. Thanks!