The spoofing interference can mislead target receiver in resulting in wrong position and time, which is a serious threat to the security of GNSS applications. An anti-spoofing method using the pseudo-range single-differences of two receivers was proposed. Using the variance analysis technique, the optimal spoofing detection variable based on the pseudo-range single-differences was deduced and the statistical character of the detection variable was analyzed. After analyzing, the parameters such as the receiver noise, the receiver baseline, and the satellite number have a large influence on the detection performance; as the receiver noise and satellite number are uncertain, the detection performance can be improved by increasing the length of baseline. When the length of baseline is 10 meters, the simulation results illustrate that the spoofing detecting probability is up to 98% if the false alarm rate is 0.01.