To improve the mixing of homogenous air-fuel in cylinder,a new fuel supply system for gasoline direct injection engine,compound fuel supply system was presented. With the three-dimensional numerical simulation method,the optimum design of low-pressure fuel injector position was investigated,and the influence of compound fuel supply system on the air-fuel mixture formation in cylinder under the cold-start condition of GDI engine was analyzed. The results showed that the air-fuel mixing process in intake manifolds and the concentration of mixture entered into the cylinder during the intake stroke were greatly influenced by the low-pressure fuel injector position. The compound fuel supply system can improve the mixing of air-fuel and the distribution of air-fuel ratio in cylinder under the cold-start condition,and reduce the HC emission.