Relationship between the target scattering function and the echo signal is deduced to hold as a Fourier transform pair by analyzing the texture of echo signal for a passive radar imaging system;then an algorithm is presented,which makes use of multiple receivers to form a synthetic aperture for passive radar imaging in the case of single external illuminator available.Due to collected data is non-uniform and sparse in Fourier space,the presented algorithm processes data in polar grid format,which can make full use of original precise data,so the quality of final image is improved.Theory derivation and computer simulation confirm the effectiveness of the proposed algorithm.