Abstract: The working characteristics of Shanghai 65m radio telescope require large active panels with high precision. A precision forming process, which is based on envelope mold, skin with crevices, releasing stress and vacuating press, is proposed to solve the difficulties in manufacturing such panels. A nonlinear finite element model is built to model the process of a panel. In the analysis, the relationship between the panel surface curvature, slot length of skins, height of stiffeners and precision is studied. According to the relationship, the structure and technical parameters of the panel are optimized. Consequently, the panel precision is better than 100 μm rms. The technique has been successfully used in Shanghai 65m radio telescope, and it can be also applied to other antenna reflectors.