The design of the barrel chrome layer in a certain type of 35 millimeter automatic grenade launcher has low pass rate and high production cost. In order to solve the problem, the author did some research on the thickness of the chromium and found its weakness. After the in-depth analysis, the author advocated to adjust the thickness of chromium and has tested it through a large number of experiments. The result shows that the method not only can shorten the production time, reduce the production cost and use less material such as chrome plating solution, water, electricity, gas, etc, but also improve the production efficiency and the pass rate.