The impact of digital receiver carrier frequency on the ranging precision is analyzed. It is pointed out that when the IF carrier frequency is an integer multiple of PN code rate, the ranging value will have a larger jitter. Based on the analysis of the relationship among the IF carrier frequency, PN code rate and sampling rate, the formula of designing high precision pseudo code ranging system from the three parts is put forward, which can be used to determine whether a certain value is suitable for the frequency of the IF carrier. The formula shows important guiding significance for the design of pseudo code ranging system.