In this paper, the deep level transient spectrums of polysilicon n-p diode depletion region have been measured by use of DLTS instrument. According to the DLTS experimental results, the uniform trapping model set by G. Baccarina etc. has been modified and the linear trapping model of the grain-boundary has been proposed. Using the modified model, the relationship between the polysilicon electrical parameters, barrier height Eb as well as activation energy Ea, and the dopping level NG can be solved iteratively. The calculation results show that the linear trapping model of the grain-boundary is possessed of theoretical reasonableness.