Gas flow distribution of reaction chamber of reactive ion etching (RIE) etcher is usually considered to be a main factor in determining both the plasma distribution and etching uniformity. Based on the continuum fluid and heat transfer models of the commercial software, Fluent(Ansys), the gas flow distribution of the reaction chamber was simulated. And then the spatial distribution profiles of the pressures above the electrode surface under the different mass flow (50～250sccm) inlet conditions , and the influence of the different GAP (L = 0.03～0.06m) of the chambers on the gas flow uniformity were discussed. The result shows that the pressure distribution above the electrode has the character which the pressure is higher in the center of the electrode and lower at the edge and increases with the rise of the mass flow of inlet. And the uniformity of the gas flow distribution is enhanced with the rise of the GAP of the chamber.