Abstract: The detection problem of dim signal is studied based on mono-frequency or narrowband dual-polarization radar system in this paper. Firstly, the descriptions of Instantaneous Polarization Projection Sequences (IPPS) of signal and noise are presented and statistics of generalized distance between random EM wave and the anticipant signa are derived. Then, utilizing the generalized distance difference of signal and noise to the anticipant signal, a novel detection algorithm is presented through polarization accumulation. In this paper, detect performance of radar system is improved obviously and more than 10dB.