private Procedure OnMouseWheel(Var Msg :TMsg;var Handled:Boolean); { Private declarations } public { Public declarations } end;var Form1: TForm1;implementation{$R *.dfm} Procedure TForm1.OnMouseWheel(Var Msg :TMsg;var Handled:Boolean); begin if Msg.message = WM_MouseWheel then begin if Msg.wParam > 0 then begin showmessage('逆时针滚动'); end else begin showmessage('顺时针滚动'); end; Handled:= True; end; end; procedure TForm1.FormCreate(Sender: TObject); begin Application.OnMessage:=OnMouseWheel; // 截获鼠标滚动事件 end;end.
或窗体的另两个WheelUp 和 WheelDown.
给你个网上下载的例子（mousep.PAS）
==================================
unit Mousep;interfaceuses
SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
Forms, Dialogs, StdCtrls;type
TForm1 = class(TForm)
Label1: TLabel; {显示wParam}
Label2: TLabel; {显示lParam}
Label3: TLabel; {显示x,y}
Label4: TLabel; {显示hwnd}
Label5: TLabel; {显示window text}
Label6: TLabel;
Label7: TLabel; {显示window class}
private
{ Private declarations }
public
{ Public declarations }
end;function sethook:bool;export;
function unhook:bool;export;
function mouseProc(code:integer;w:integer;l:longint):bool;export;var
Form1: TForm1;
idhook:longint;
formok:bool;
implementation
{*********************************************************************
声明安装函数setWindowsHookEx()，
在Ｄelphi中如果用函数setWindowsHook()则不需声明。
微软说函数setWindowsHook已在Windows3.1中废弃，为与Windows3.0兼容仍保留。
实际上该函数setWindowsHook在Windows3.1和Windows95中仍可使用。
{*********************************************************************}
function setwindowsHookEx(id:integer;proc:tfarproc;hinst,htask:thandle):
longint;far;external 'user';
{$R *.DFM}{安装鼠标钩子函数mouseProc}
function sethook:bool;
var
hinst:thandle; {该动态连接库自己的模块局柄}
proc:tfarproc; {鼠标钩子函数mouseProc的地址}
begin
{在动态连接库中创建form1}
if formok=false then form1:=tform1.create(application) else exit;
formok:=true;{安装form1 后,设置formok,不许再安装form1}
{动态连接库的application指：调用动态连接库的主程序}
form1.show;{不让用系统菜单来双击关闭Form1}
form1.BorderIcons:=form1.BorderIcons-[biSystemMenu];hinst:=getModuleHandle('mousedll');
{得到mousedll.dll的模块局柄，即该动态连接库自己的模块局柄}proc:=getProcAddress(hinst,'mouseProc');
idhook:=setWindowsHookEx(WH_MOUSE,proc,hinst,0);
{用WH_MOUSE参数安装鼠标钩子后，移动鼠标时，系统自动调用mouseProc钩子}
if idhook =0 then sethook:=false else sethook:=true;
end;{解除鼠标钩子函数mouseProc的安装}
function unhook:bool;
begin
if formok=true then form1.free else exit; {检查form1是否已经关闭}
formok:=false;{关闭了form1,设置formok=0}
if idhook=0 then exit;
unhookWindowsHookEx(idhook);
unhook:=true;
end;{mouseProc不由应用程序调用，而是在鼠标移动后，由系统调用}
function mouseProc(code:integer;w:integer;l:longint):bool;
var
p:^TMouseHookStruct;
poff:word;
pseg:word;
pmemo:pchar;
begin
if code<0 then begin
mouseProc:=true;
CallNextHookEx(idhook,0,w,l);
end;
if code=HC_NOREMOVE then form1.caption:='HC_NOREMOVE';
form1.caption:='mouse hook';
mouseProc:=false;
{显示系统传来的wParam参数，w是各种鼠标消息的标识符 }
form1.label1.caption:='wParam='+intTostr(w);
{显示系统传来的lParam参数，l是MOUSEHOOKSTRUCT结构的地址}
form1.label2.caption:='lParam='+intTostr(l);poff:=loword(l); {得到l的低１６位}
pseg:=hiword(l); {得到l的高１６位}
p:=ptr(pseg,poff); {合成指向MOUSEHOOKSTRUCT结构的指针}{显示屏幕上鼠标的Ｘ，Ｙ坐标}
form1.label3.caption:='pt.x='+intTostr(p^.pt.x)
+' pt.y='+intTostr(p^.pt.y);
{显示屏幕上鼠标下的窗口局柄}
form1.label4.caption:='hwnd='+intTostr(P^.hwnd);pmemo:=stralloc(20);
getWindowText(p^.hwnd,pmemo,20-1);
{显示鼠标下窗口的标题栏}
form1.label5.caption:=strPas(pmemo);getClassName(p^.hwnd,pmemo,20-1);
{显示鼠标下窗口的类}
form1.label6.caption:=strPas(pmemo);strDispose(pmemo);end;
end.
Procedure OnMouseWheel(Var Msg :TMsg;var Handled:Boolean);
{ Private declarations }
public
{ Public declarations }
end;var
Form1: TForm1;implementation{$R *.dfm}
Procedure TForm1.OnMouseWheel(Var Msg :TMsg;var Handled:Boolean);
begin
if Msg.message = WM_MouseWheel then
begin
if Msg.wParam > 0 then
begin
showmessage('逆时针滚动');
end
else
begin
showmessage('顺时针滚动');
end;
Handled:= True;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
Application.OnMessage:=OnMouseWheel; // 截获鼠标滚动事件
end;end.