Due to absorption and scattering of light in the underwater environment, the visibility and contrast of image will be reduced, the image usually gets blurred, and color cast，the quality and reliability of image processing will be affected, so the underwater image enhancement is necessary preprocessing stage. This paper presents an improved unsupervised color correction method (UCM) for underwater image enhancement. The improved UCM algorithm firstly makes color correction by statistical method and solves color distortion. Then，the contrast stretching is carried out to R, G and B color channel of RGB color model with different strategies, the display range of each channel is expanded, and the contrast is enhanced. Finally, bilateral contrast stretching is conducted to saturation component S and intensity component I of HSI color model, to increase the saturation, and to solve the lighting problem by increasing the stretching strength. Compared with other algorithms, the proposed algorithm can produce better underwater image enhancement effect.