Perhaps some triangle patchs of "ROAD" is too large in my model of scene,they are filpped by hardware(i think) sometime and can't be drawn when a majority part of them is not in viewport and other part is in.
But it 's error.
So i want to ask how to close hardware flipping or other solutions?
It's called tessellation, and you'll find many wonderful articles about it on the web. It's been around for a LONG time. It's one of those topics any 3D programmer should already know. :)