<!DOCTYPE HTML> <html lang="en-US"> <head> <meta charset="UTF-8"> <title>easonjim</title> <script src="scripts/jquery.js" type="text/javascript"></script> </head> <body> <select id=\'province\'> <option value=\'6\'>66 <option value=\'7\'>77 <option value=\'8\'>88 </select> <input type=\'button\' id="btn1" value=\'setPi\'> <script type="text/javascript"> $(\'#province\').on("change", function () { alert($(\'#province\').get(0).selectedIndex); }); $(\'#btn1\').on("click", function () { $(\'#province\').get(0).selectedIndex = 1; $(\'#province\').trigger("change"); }); </script> </body> </html>