The parafoil system is widely used in spacecraft recovery and precision airdrop because of its excellent gliding capability, controllability and stability. The dynamics of controllable parafoil system has been a hot spot issue in order to design the control algorithm. In this paper, a dynamical model with eight-degree-of-freedom for parafoil system is established based on Lagrange multiplier method. Based on this model, the motion of parafoil system in airdrop condition is simulated. The efficiency and accuracy of this model are verified by comparing calculation results with the airdrop test data. 