Abstract: Injection molding of front cover and front panel of mobile phone with different volume two-cavity is regarded as the research object , based on numerical simulation software MPI ,the study is distributed into the contrastive analysis of different runners. The influence of three typical injection on three important process factors , such as injection time，conversion pressure and clamping force are analyzed, then the appropriate runner design is selected according to the demand for products, at last the runner size is ascertained based on the ratio of two cavity filling time . Optimization of the runner makes the melt flow into the volume cavity keep flow balance and minimize the shortcomings of parts.

Key words: fiow balance, injection molding, mould, runner, flow simulation