When the sampling covariance matrix contains the desired signal, the model mismatch will greatly reduce the performance of MVDR (minimum variance distortion response) adaptive beamforming algorithm. A robust adaptive beamforming algorithm based on spatial smoothing difference algorithm (SSDA) is proposed in this paper. The algorithm first obtains the prior knowledge of the number of sources through the spatial smoothing difference algorithm, then searches the wave crest of the MVDR spatial power spectrum to obtain the expected signal, and finally removes the expected signal covariance matrix from the sampling covariance matrix. The simulation results show that under the condition of high signal to noise ratio input, the output signal to interference plus noise ratio of the improved algorithm has been greatly improved after removing the expected signal, which is 2 ~ 3 times higher than that of MVDR algorithm.