It is the core problem in laser detection system keeping low false alarm probability while ensure the detection distance. Based on CMOS imaging laser detection system, the main factors arousing false alarm were analyzed, which is scene noises and strong light disturbances. For these, three approaches of false alarm rejection technology were presented, which were spectrum filtering, increasing image frame frequency to decrease integral time and frame subtraction technology. The test result showed that the false alarm probability was greatly decreased with the same detection threshold, which obtained preferable false alarm rejection effect.