unit Unit1;

interface

uses 
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type 
TForm1 = class(TForm) 
private 
{ Private declarations } 
procedure WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo);
//取得最大化的消息
message WM_GETMINMAXINFO;
public 
{ Public declarations } 
end;

var 
Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo);
begin 
  inherited;
  with Msg.MinMaxInfo^ do
  begin
    ptMinTrackSize.x:= form1.width;//最小化时的宽度
    ptMaxTrackSize.x:= form1.width;//最大化时的宽度
    ptMinTrackSize.y:= form1.height;//最小化时的高度
    ptMaxTrackSize.y:= form1.height;//最大化时的高度
  end;
end;
end.

http://blog.csdn.net/diligentcatrich/article/details/7008785