uses wininet;

function CheckUrl(url: string): Boolean;
var
hSession, hfile: hInternet;
dwindex, dwcodelen: dword;
dwcode: array[1..20] of Char;
res: PChar;
begin
Result := false;
if Pos('http://', LowerCase(url)) = 0 then url := 'http://' + url;
hSession := InternetOpen('InetURL:/1.0', INTERNET_OPEN_TYPE_PRECONFIG,
nil, nil, 0);
if Assigned(hsession) then
begin
hfile := InternetOpenUrl(hsession, PChar(url), nil, 0, INTERNET_FLAG_RELOAD, 0);
dwIndex := 0;
dwCodeLen := 10;
HttpQueryInfo(hfile, HTTP_QUERY_STATUS_CODE, @dwcode, dwcodeLen, dwIndex);
res := PChar(@dwcode);
Result := (res = '200') or (res = '302'); //200,302未重定位标志
if Assigned(hfile) then
InternetCloseHandle(hfile);
InternetCloseHandle(hsession);
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
if CheckURL('http://www.delphitop.com/123.txt')then
showmessage('fang')
else
showmessage('error');
end;