In this paper a method is proposed to estimate the unknown parameters of nonlinear map based on the discrete variational principle, which can be applied to all map chaotic systems governed by the following equation: xk+1 = F(xk,). Numerical simulations on the well-known Logistic map and Henn map are conducted and all unknown parameters of the two discrete chaotic systems are identified respectively. Simulation results show that the discrete variational method is effective for parameter identification of the map chaotic system.