In this paper a new refraction compensation method is presented for the underwater 3D measurement on the basis of a structured light sensor.The parameters of the system calibrated by the planar grid target method become invalid because of the refraction between two different kinds of media.This method can measure the underwater object on the basis of underwater 3D measurement model by correcting the equation of the laser plane and the imaging of object in the CCD after refraction.A measuring system has been designed for the experiments,and the results prove that the method works well with high accuracy.