I did more test on the Near Clip Plane setting, and here’s what I v found:
when < 0: everything is invisible, but you can still see then in wireframe;
when = 0: render wrong depth as I mentioned in the former post;
when > 0 but very small like 0.001: some stripes appear(shadow problem?)
when 0.01, the gaps between stripes age getting smaller.↓↓↓
when 0.1, looks normal. maybe the 0.1 is the smallest number for Near Clip Plane while it still works fine?