In view of the characteristics such as non-uniform brightness,low s ignal to noise ratio as well as the low contrast of the underwater dam crack image,this paper brings up a novel dam crack image enhancement algorithm,which adopts the simulation of underwater biological vision.With ref erence to the brightness adjustment characteristics of the biological vision,this algorithm also improve s the non-uniform brightness of underwater dam crack image.Furthermore,in order to improve the low signal-to -noise ratio and solve the problem of low contrast of dam crack image,on the basis of lateral inhibition enhancement mechanism of the "horseshoe crab fish",we introduce the adaptive asymmetric narrow strip guidance models,w hich can help to enhance the linear characteristics of the crack image.The theoretical and the experimental results got from this paper show that the proposed algorithm can significantly eliminate the noises of the underw ater image,and also better improve the definition of the image from the physical standpoint.And at the sam e time,by strengthening the edges of crack image and enhancing the subtle liner structures of interest in th e crack image,this algorithm improves the contrast of the interesting areas,whic h is of great significance for the subsequent crack feature extraction.