Set the swf file attribute to transparent and add it to the flash parameter. If you use dreamweaver and select the swf file, there will be a "parameter..." button on the properties panel (at the bottom of the panel). Click it, add wmode below the "parameter" on the left in the pop-up box, enter transparent to the corresponding value on the right. After confirming it, it will be fine.
Or, directly in the Flash Object, add:
<param name="wmode" value="transparent">
Or, directly in the Flash Object, add:
<param name="wmode" value="transparent">