Interference of dual sources is an effective means of counteracting passive radar seeker (PRS). In the practice，the power of dual sources is hard to be the same, so it is possible for PRS to counteract interference of dual sources. In far field, PRS will not follow the power centroid and point the higher power source of double sources as long as the number of the seeker accumulating data is large enough. It is proven by theoretical analysis and simulation experiments. And the formulation of the number of the seeker accumulating data is given.