swfobject.embedSWF("about:blank", "myContent", "550", "400", "9.0.0","expressInstall.swf",flashvars);
document.getElementByID('myContent').movie = "xxx.swf";
如果上诉语句不能解决,则换线程:
setTimeout(function(){document.getElementByID('myContent').movie = "xxx.swf"},0.1);