To improve the wavefront detection accuracy of a liquid crystal adaptive optical system, a correction method for the Tip/Tilt Mirror(TTM) in the liquid crystal adaptive optical system was researched. The physical characteristics of each ingredient in the adaptive optical system were analyzed, and the basic structure of the TTM model was given based on the Lagrange equation. Then, the model parameters were acquired by using modified subspace identification method, and the frequency domain characteristics of a subspace model were corrected by nonlinear least squares algorithm. After correction, the transfer function precisions are 0.024 5 dB for the amplitude and 1.900 8° for the phase in middle and low frequency domains. Furthermore, Smith predictor was introduced to solve the time delay problem during TTM correction. The model obtained by space identification was used in the simulation and experimental verification by Smith and PID . The experiment result is coincided with simulation result. It is shown that PID with the Smith predictor is superior to traditional PID, and the error residual bandwidth of Smith predictor is enhanced by 23.97% as compared with that of the traditional PID. Finally, a signal of turbulence Tip/Tilt was generated for a correction experiment, and the experimental result shows that the control precision of PID with Smith predictor is improved by 21.03% compared with that of traditional PID, which verifies that the proposed method optimizes the correction accuracy of the TTM and ensures the wavefront detection accuracy of the liquid crystal adaptive optical system.