The 3C (Computer, Communication and Consumer) product has the properties of being light, thin, short and small. In this study, numerical simulations of three-dimensional injection molding are used for thin-walled product. The governing differential equations are discredited by using control volume finite element method. This research points out the processing phenomenon of electronic dictionary battery covers in thin-walled injection molding. This research emphasizes the gate design of thin-walled injection molding for PC+ABS materials. The results show that the gate for single point of two sides is suitable on thin-walled injection molding by numerical simulation. The results also show that the processing is very well for thin-walled injection molding by numerical simulation.