Abstract: The paper introduced a design scheme of motor protection device based on dual-CPU of DSP56F807 and W78E516B, and analyzed circuit designs of main control board and man-machine interaction board and protection algorithm of the device. The device uses DSP56F807 to realize functions of multi-channel AD conversion, electricity-quantity calculation, kinds of protection algorithm, real-time clock control, data storage, CAN communication and output control of switching value of relay, uses W78E516B to realize function of man-machine interaction, and uses Fourier algorithm that can compensate any decaying time constant and filtrate decaying DC component to improve precision and correctness of motor protection algorithm. The experimental result showed that over-current protection algorithm of the device is good in sensibility and reliability with better running effect.