A new enhancement algorithm is proposed aiming at the problems of uneven illumination and low contrast of underwater image.Firstly,background removing method is utilized to correct the uneven illumination.After that an improved Butterworth homeostasis filter is used to enhance the underwater image.It can repress the low frequency components and enhance the high frequency components so as to get high contrast underwater image.Experiment results show that the proposed method can not only balance the illumination but also improve the image contrast.It has a better performance compared with other algorithms.