Abstract: On the basis of the development of the multi-fluid cavity filling flow mechanism in the co-injection molding，general Hele-Shaw model and Volume-of-Fluid technique to establish the theoretical model for numerical simulation to describe the cavity filling process in co-injection molding are used，and a stable effective numerical solution algorithm for solving the theoretical model is presented. The numerical simulation of the effect of the material parameters and molding process parame-ters on co-injection molding is implemented，the relation be-tween those parameters and the patterns of the layer interface is established. The results of a case study of numerical simulation have a good agreement with the experimental results given in some literatures.

Key words: Cavity filling, Co-injection molding, Numerical simulation, Thermomechanical model