I use gtk.EntryCompletion to implement the autocomletion function.
But the list is so long that the pop-up window touches the bottom of screen.
And I cant find the method of set the height of pop-up window in doc of pygtk.
How to set the height of pop-up window in gtk.EntryCompletion?
I don't know if this applies to gtk.EntryCompletion widgets, but for cell like widgets you can control their height with the cell.set_fixed_height_from_font(True) method. 
Look at the gtk.CellRendererText API for details.
pygtk: How to set the height of pop-up window in gtk.EntryCompletion