Abstract: Mathematic models were established to represent the curing step of thermoset composites, a finite element formulation for three-dimensional transient cure simulation of composite structures was introduced and a simulation code CURESIM was developed based on the formulation. The simulated results match the experimental results well, which demonstrates the mathematic models and numerical algorithm are of high reliability. The temperature and degree of cure distribution can be obtained at any time by the simulated code. The numerical simulation method can be used to optimize the curing temperature cycle, which can improve the quality of composite products.