The figure evaluation method is put forward which is the fast evaluation method of interpolation errors of the encoder with high precision. Wavy generator is formed on photoelectrical signal of the encoder. The criteria for judging the quality of a fitting curve is also established. High-precision encoder moiré fringe photoelectrical signal is analyzed by using figures evaluation method, and the curve of interpolation errors is gotten. Compared with interpolation errors which are received from traditional detect method, the experimental result indicates: the figure fitting method can be applied to evaluate interpolation errors of high-precision encoder, the equipments is convenient and the examination method is efficient and feasible. Data processing can be realized by valuation analysis software in short time. The system can be used in the working field to avoid the influence of the speed，and has important meaning to the research of high-precision encoder’s dynamic precision characteristics.