In order to solve the problems of missed alarm and slow response speed in the existing laser alarm system due to untimely data processing, a rapid extraction algorithm of spot center based on projection segmentation was proposed. According to the characteristics of the horizontal uniform distribution of spots at all levels in the diffraction images, a method of rapid extraction was proposed by projecting to the coordinate axis and calculating the center coordinates of light spot respectively. The proposed algorithm was deployed to the FPGA hardware system, so as to enable the alarm system to complete the task of extracting the center coordinates of the spot within a frame image transmission cycle, which improved the image processing efficiency and realized the efficient alarming. Experiments show that the maximum error of spot center coordinate extraction is 1 pixel, and the response time of the alarm system is 17.453 ms. By optimizing the image processing algorithm, the response time of the alarm equipment is shortened, and the rapid and accurate alarm of the incoming laser is realized.