In order to enhance the contrast of short.wave infrared image and improve the recognition ratio of target, a method of grayscale stretching algorithm based on Field Programmable Gate Array(FPGA) is proposed in this paper. According to the similar grayscale distribution between two consecutive frames, the parameters needed for image stretching are obtained by calculating the grayscale distribution of the previous frame, so as to process current frame, and real.time processing is achieved. In the grayscale statistics module, the design of non.frequency.multiplied pipelined logic is applied using the Block RAM resources on the FPGA chip. The proposed method avoids clock domain crossing in the grayscale distribution calculation process, reduces the complexity of the state machine, and improves the maximum operating frequency of the system. A domestic 320×256 InGaAs detector and an experimental platform based on Xilinx Artix-7 series FPGA are utilized to carry out the experiment. The results show that this method can effectively improve the contrast of the short.wave infrared image, which has the advantages of less resource utilization, fast computing speed, low cost, high portability, etc. and meets the design requirements of the real.time grayscale stretching of the short.wave infrared camera.