Abstract: The paper firstly analysed the character of underwater light image——very low contrast and resolution.The main factors affecting the quality of underwater light image are backscatter and small-angle forward scatter.A mathematical model of underwater light image was built.Then a special adaptive enhancement filter was analysed and devised for such image.The algorithm has three shortcomings:(1)"ring"response;(2)"salt and pepper"noise;(3)simultaneous enhancement of high frequency noise and image details.But our improved adaptive enhancement filter algorithm,as shown by experiment,has surmounted them.