Based on the finite element method(FEM) for the dynamical analysis of piezoelectric truss structures, the expressions of safety margins of strength fracture and damage electric field in the structure element are given considering electromechanical coupling effect under the joint action of electric and mechanical load. By importing the stochastic FEM,reliability of piezoelectric truss structures is analyzed by solving for partial derivative in the process of solving dynamical response of structure system with mode-superposition method. The influence of electromechanical coupling effect to reliability index is then analyzed through an example.