Conformal antenna array can be utilized to receive the incoming signal for passive radar seeker in multimode compound guidance mode. Generally，conformal antenna is in linear polarization， surrounded by the elastomer，which will lead to polarization diversity. The receiving signals model of conformal antenna array is built. The effects of antenna polarization diversity on the interferometer direction finding performance are studied. The precondition of interferometer method getting right result is analyzed. Finally，the effectiveness of conclusion is verified by the computational simulation results. This paper gives an idea which will make PRS get right direction finding result，to solve the polarization diversity of conformal antenna array.