Whether it is feasible to perform an integrated simulation for structural analysis, process simulation, as well as warpage calculation based on a unified CAE model for gas-assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same CAE model used for process simulation regarding filling and packing stages were developed to simulate the cooling phase of GAIM considering the influence of the cooling system. The cycle-averaged mold cavity surface temperature distribution within a steady cycle is first calculated based on a steady-state approach to count for overall heat balance using three-dimensional modified boundary element technique. The part temperature distribution and profiles, as well as the associated transient heat flux on plastic-mold interface, are then computed by a finite difference method in a decoupled manner. Finally, the difference between cycle-averaged heat flux and transient heat flux is analyzed to obtain the cyclic, transient mold cavity surface temperatures. The analysis results for GAIM plates with semicircular gas channel design are illustrated and discussed. It was found that the difference in cycle-averaged mold wall temperatures may be as high as 10 degrees C and within a steady cycle, part temperatures may also vary similar to 15 degrees C. The conversion of gas channel into equivalent circular pipe and further simplified to two-node elements using a line source approach not only affects the mold wall temperature calculation very slightly, but also reduces the computer time by 95%. This investigation indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAF : model, resulting in great computational efficiency for industrial application.