Abstract: Under the trend of complex electromagnetic environment and weapon system concealment, the target echo is often submerged in noise interference and cannot be detected accurately. The passive radar has attracted wide attention because it can cope with the threat of electronic warfare, stealth technology and anti-radiation missile. However, the passive detection methods are limited by the characteristics of the exploited illuminator, and sometimes long term integration methods are difficult to improve the detection performance effectively. According to the above problems, we propose a detection method of weak targets of passive radar. This method uses single pulse as the processing object, and adopts the probability statistics knowledge to record every detection result after the threshold detection during the observation time, and performs the target detection by the distribution of detection results in the probability histogram. Numerical experimental results show the proposed method can effectively detect the weak target for passive radar, and can be a feasible solution for practical implementation.