Abstract: Traditional method is using a collimator and polyhedron for encoder accuracy detection with shortcomings of low efficiency, which requires experienced master. Encoder error detection adopts binary light bars, when rotated encoder forward, the light bars will carry normal. However, this method is inefficient, and also resulting in an error of judgment. The automatic detection system for photoelectrical encoder was designed. Motor fiducial encoder and certified encoder were coaxial. As position and speed feedback, fiducial encoder's resolving was 0.077. DSP was the control core, automatic detection system was working in speed and position mode. Precision demarcating was in position mode while error checking was in speed mode. The automatic detection system was used to detect two 14 Bits encoders, comparing with collimator detection system, experimental results show that the system works effectively and properly. The accuracy detection and error code checking can be performed simultaneously, improved the detection efficiency and shorten the design cycle of the encoder. Other models encoder debugging and testing can be extended.