In composite steel plate shear walls system, steel web plates can be strengthened by adding a number of layers of fiber reinforced polymer laminate or concrete on one or both sides of the web plate. In this paper, nonlinear behaviour of strengthened steel plate shear wall by means of glass fiber reinforced polymer laminates have been numerically investigated. In that regard, the tested ½ scaled one-story un-stiffened steel plate shear walls have been selected and simulated using finite element method, based on the available experimental data in the literature. Non-linear large displacement analyses on the finite element model have been carried out and the results presented. The shear capacities and hysteresis curves of the experimental and numerical unstiffened steel plate shear wall are compared. It is found that the simulation outcomes have showed good agreement with the experimental results. After calibration of the numerical model, steel web plate is strengthened by GFRP laminate, and effects of GFRP laminate on the seismic behavior of strengthened steel plate shear walls are investigated. The results indicate that with strengthening infill steel plate on the steel plate shear walls, yield strength, ultimate shear capacity, secant stiffness and cumulative dissipated energy of SPSWs can be significantly increased.