Abstract: In order to improve the resolution,contrast ratio and the robustness against the noise of the minimum variance(MV) method,an improved minimum variance(IMV) method was introduced.The received signal was divided into desired signal and noise signal at first,then the adaptive weighting vectors were obtained by minimizing the output power of the desired signal.In addition,a pair of constrained conditions were added to the steering vector to further enhance the robustness ability against the noise.Points target and cyst phantom were simulated under both the plane wave mode and the synthetic mode.The simulation results showed that the lateral resolution of the proposed method was improved by a factor of 2 in plane wave mode,and the contrast ratio was increased over 8 dB in synthetic aperture mode on the basis of eigenspace-based minimum variance(ESBMV).Furthermore,the proposed method was far better than traditional delay and sum(DAS) algorithm.Finally,the experiment was conducted based on the real ultrasound data.The results indicated that the proposed method had a better resolution,contrast ratio and was more robust to the noise,which showed its potential application to enhance ultrasound imaging quality.