Closed loop wavefront residual error of adaptive optical system consists of the uncompensated turbulence error and closed loop noise. The measured closed loop wavefront residual error is analyzed by using open loop and closed power spectrum. When the system noise is considered, the measured reconstructed phase error and the closed loop wavefront residual error are different. Based on the difference of their power spectrum, a method of evaluating the closed loop wavefront residual error is proposed. The comparison of the reconstructed phase error, which is calibrated in high resolution adaptive optical system of 1.2 m telescope, and the closed loop wavefront residual error is given.