According to recent changes in industry for the semiconductor device, a gap between patterns in wafer is getting narrow. And this narrow gap makes a failure of uniform deposition between center and edge on the wafer. In this paper, for solving this problem, we analyze and manipulate the gas flow inside of the HDP CVD chamber by using CFD(Computational Fluid Dynamics). This simulation includes design manipulations in heights of the chamber and shape of center nozzle in the upper side of the chamber. The result of simulation shows 1.28 uniformity which is lower 3% than original uniformity.