When GNSS array anti-jamming performance is tested in microwave anechoic chamber, the power of multipath interference signal is still stronger than the navigation signal after absorption and attenuation. Whether the multipath affects the anti-jamming performance is an important factor of the test reliability. Based on the signal receiving model of antenna array, focusing on the covariance matrix of the received signal, the relationship between multipath signal and eigenvalue and eigenvector is analyzed in the paper. Then, based on power inverting model, the influence of multipath signal is simulated. The results show that when the strength difference between the interference and its multipath is less than a certain value, the null point of the array antenna will be pulled from the actual position; However, with the increase of the strength difference, the influence of multipath on the position of the null point decreases gradually.