In order to improve the torque of engine full load characteristics, especially for the engine torque at high speed, the genetic algorithm combining with the weighted sum method is adopted to optimize the performance of a high-speed gasoline engine. Firstly the simulation model is built by software GT-power. The simulated values are contrasted with the tested values at the same operating condition. The results show the correspondence of the calculated values with tested values. So it proves that the simulation model is reliable. According to the importance of torque at each speed, a corresponding weight coefficient is got. Using the weighted sum method to construct an evaluation function, the multi-objective optimization problem is transformed into a single one. The resonant cavity volume intake V, the intake manifold length L and diameter D, intake advance Angle θi and exhaust advance Angle θe are selected as the optimized variables, and the weighted average torque is selected as optimized object. At last the simulation model is optimized by genetic algorithm. The results show that the method of weighted sums combined with genetic algorithm can quickly search the optimal solution and realize the multi-objective optimization. Through correlation analysis, we can understand linear correlation between the optimization variables and optimization target. At the same time, the simulation model is also optimized by the use of the traditional single variable optimization method. Then the results optimized by the two different methods are contrasted.