The default is black when you render
 

How to change the default color of black in render global ?
Pls help me.

To do this you need to select the camera you want to render with then go in to the attribute editor for the camera, if you scroll down a little there should be a tab for "environment" click to open the tab and you will be able to change the color or insert a image plane. I've attached a picture of what you need to look for:

http://gladiatorjedi.tripod.com/ColorchangeMaya.jpg

thank you very much