It is significant to realize effective single underwater image restoration for acquiring clear image in underwater exploration and underwater environment monitoring field. Most existing algorithms use dark channel priors to restore images, which lead to inaccurate estimates of the background light and transmission map. Hence, a novel method with adaptive background light estimation and nonlocal prior was proposed. Firstly, the candidate water light regions could be obtained by a threshold segmentation algorithm owing to the fact that water light regions have the properties of flat and high brightness. Then, the water light value could be decided from the candidate regions by the dominant tone of the input image. Secondly, the nonlocal prior was built to estimate the transmission map by taking into account the wavelength dependence of the attenuation. Finally, in order to remove the additive noise from the medium and microorganisms, a minimal optimization problem with the solution strategy of guided filter was proposed for obtaining the de-noising result. The experimental results verify that the proposed algorithm not only ensures operation efficiency, but can also estimate the correct transmission map. In general, the restoration precision has improved by 18% compared with the existing algorithm. It can be used in the engineering practice of restoring a single underwater image.