Abstract: Exploring high-power gas engines to generate electricity by burning biogas as well as other green energy sources has been an important task in current internal combustion enginec industry. The gas engines are sensitive to equality of the charge of every cylinder. The power, emissions and reliability of the gas engines are influenced by the unequal charge frequently. The flow field of intake system of CW6200 gas engine was simulated in this paper by using CFD technique. The intake uniformity of each cylinder was studied by analyzing the pressure field and velocity field of the flow area, and the flow resistance of the intake system was also researched. The optimized intake system was designed by analyzing the calculation results. The numerical analysis and performance tests of the gas engine showed that the gas engine had better power performance when adopting two-stage resonance system. The absolute value of the flow nonuniformity of each cylinder was less than 3 percent, and the absolute value of the exhaust temperature nonuniformity of every cylinder is less than 2.5 percent. So the conclusion can be reached that the two-stage resonance system can improve the intake uniformity of the premixing gas engine effectively and enhance the performance of the engine.