Based on the finite element dynamic equations of piezoelectric smart structure, an inverse method of impact identification was presented. In this method, the least squares optimization algorithm was applied to minimize the least squares between the target value and measured value by using the backward sweep iterative calculation and forward sweep iterative calculation. The force history and location of unknown impact could be finally estimated. The finite element model of a simply supported piezoelectric smart plate under a known impact load was built to validate the effectivity of this finite element inverse method. The results indicates that the precision of this method is accurate for engineering calculation requirements, and this method is applicable to the impact identification of smart structure with complex shapes and boundary conditions.