Considering the low contrast,fuzzy edge and strong noise of underwater images,an underwater image enhancement algorithm based on nonsubsampled Contourlet transform (NSCT) and multi-scale retinex is proposed. The underwater image is decomposed by nonsubsampled Contourlet transform. Then multi-scale Retinex (MSR) is used to enhance the image’s global contrast in the low frequency subband,and an improved Sigmoid function is used to process the coefficients at each scale in the directional bandpass subbands respectively,which suppresses small coefficients and enhances large coefficients by threshold denoising method. Finally,the enhanced coefficients are reconstructed to obtain enhanced image. Compared with the other traditional methods,the approach reduces the noise of original images,improves the contrast of the image,enhances object’s contour and achieves higher quantitative contrast assessment indicator.