In order to solve the problems of low checking efficiency, low precision and high checking difficulty of surface caused by the oversize of sub-lens structure of solar energy concentrating mirror in the process of manufacture and assembly, a detection method of mirror surface shape error based on laser imaging is proposed. In this method, image processing technologies are employed to analyze the imaging of laser dot matrix. The coordinate values of the mirror coordinate system are deduced when the corresponding incident light array occurs specular reflection by distinguishing the position of reflection imaging array points with different laser beams at the image plane coordinate system. The shape error of the whole reflecting surface is obtained by substituting the above incident point array coordinate values into standard paraboloidal equation to fit and calculating with the steepest descent iterative method. By comparing the measurement results of reflector with coordinate measurement machine, the result shows that the measurement accuracy of the proposed method can reach 0.8 mrad.