Abstract: A mathematical model of heat transfer in part was established to simulate thermal behavior of GMT parts during compression molding, coupled with non-isothermal crystallization kinetics of polypropylene. A finite-element method was used to solve the model. The distribution of internal temperature and crystallinity of GMT parts were calculated, based on the non-isothermal crystallization model. The effects of mold temperature and the part thickness on cooling and crystallization processes were considered. The simulated results agreed well with experimental data. The proper mold temperature should be about 80 ℃, and the mean crystallinity of the resin should be controlled in the range of 0.51~0.55.