Abstract: The accuracy of secondary monopulse surveillance radar OBA(off-boresight angle) is one of the most important factors affecting radar angle measuring precision.In order to improve radar angle measuring precision,some algorithms of estimating OBA are presented.The first method is a direct method,which requires aircraft flight test;the second method is a statistical method,which requires fixing of the replying device;the third method is to constructa linear equation set,which is based on the relation ship between the franspender reports.Considering engineering application,this paper puts emphasis on the last two algorithms.The experiment results show that the proposed methods are effective in estimating OBA.