Abstract:A method finding the global optimum value of misalignment is presented.It is used to increase the accuracy of range alignment.There exist the drift and jump erros when use the classical amplitude correlation method to aling the envelope of the echoes.Sometimes,these errors are so great that they are as large as the sidth of several range bins.So the quality of image is badly affected.By usign global optimum method,the range alignment is more accurate,teh drift and jump phenomena of echo envelope are decreased and the quality of the image is improved.Form the image result of real measured data,it can be seen that this method is much better than the classical method.