In order to solve the problem of low detection accuracy of infrared dim targets under complex background,a method of infrared dim target detection based on visual contrast mechanism was presented.Firstly,the gradient saliency map of the infrared image is extracted by the 8 direction gradient equation,and binarization processing is carried out for them.According to the size characteristics of small targets,the gradient saliency map is optimized to eliminate the isolated noise points and the larger saliency area of the background gradient.The visual contrast mechanism is used to calculate the local contrast of the optimized saliency map,and then the false target is eliminated by the threshold processing to achieve the infrared dim target detection.The simulation results show that the proposed algorithm has higher detection rate,lower false alarm rate and short single frame detection time in the case of low SNR.