Abstract Active reflectors are often used to compensate the surface distortion caused by environmental factors that degrade the electromagnetic performance of large high-frequency reflector antennas. This is crucial for maintaining high gain working for antennas. A distortion compensation method for the active reflector of large dual-reflector antenna is proposed. A relationship is established between the surface deformation and the optical path difference for the primary reflector by the geometric optics. Subsequently, employing finite element analysis, a polynomial fitting approach is used to describe the impact of adjusting points on the reflector surface based on the coordinates of each node. By standardizing the positions of various panels on the reflector, the fitting equations can be used to the reflector panels of similar shapes. Then, based on the distribution characteristics of the primary reflector panels, the actuators adjustment equation is derived by the influence matrix method. It can be used to determine the adjustment amount of actuators to reduce the root mean square (RMS) of the optical path difference. And, the least squares method is employed to resolve the matrix equation. The example of a 110m aperture dual-reflector antenna is carried out by the finite element analysis (FEA) and the proposed method. The results show that the optical path difference is reduced significantly at various elevation cases, which indicates that the proposed method is effective.