<!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>