Abstract: To accurately simulate the process of fragment penetrating bulletproof vests and reveal the interaction mechanism, a constitutive model suitable for simulating the mechanical properties of soft bulletproof vests was developed based on the user subroutine VUMAT of ABAQUS, and the finite element model of spherical fragment penetrating soft bulletproof vest was established. The numerical simulation results are in good agreement with the experimental results. The material failure mode data in the constitutive model show that the unidirectional fiber cloth mainly fails in fiber tension, matrix tension and compression. In the initial stage of steel sphere penetrating bullet proof vest, the stress contours on the unidirectional fiber cloth generally present a regular circle or ellipse, and then slowly diffuse around. In the penetrating process, there is obvious fiber delamination failure. Moreover, the delamination phenomenon also appears in the fiber layer which is not pierced. The delamination area decreases first, then increases, and then decreases from the attack surface to the back surface.