According to the process of carrier phase data observation, the cycle slip will cause the incorrect of high precision positioning. Combined with the theory of high difference and autocorrelation function, a method based on high difference and autocorrelation function is put forward to judge whether there occur the cycle slip or not, and the method is introduced and analyzed in this paper. This method has a profound theoretical basis, according to the degree of correlation feature of high difference sequence and the normalized autocorrelation function of cycle slip detection, the experimental results show that this method can effectively detect cycle slips and judge slips of the position, so as to improve the reliability and accuracy of observations.