An improved model is proposed based on the transient power law model under Human Body Model (HBM) stress. This model can predict the gate oxide breakdown statistically under HBM stress. Through HSPICE simulation tool, the corresponding DC effective voltage on the MOS can be calculated. The scatter chart of the precharge voltage of the HBM circuit with the effective DC voltages of the MOS shows a linear relationship. Using the Laplace transform, the linear relationship is proved. Compared with the existing transient power law model, the improved model reduces the computational complexity under the HBM stress and is easier to predict the MOS gate oxide breakdown statistically. The proposed model provides an important reference for the evaluation of the reliability of the MOS gate oxide under the impact of HBM.