The utility model provides a prevent direction changing protection device of motor for insert the power supply loop of a motor, this power supply loop has the three -phase inlet wire, include: insert an open -phase protection return circuit of an arbitrary looks inlet wire in the three -phase inlet wire has a motor open -phase protection ware and a normal indication lamp of series connection in this open -phase protection return circuit, with the parallelly connected electrical control return circuit in open -phase protection return circuit, including a tripping operation alarm circuit and with the parallelly connected warning experimental loop of tripping operation alarm circuit. Can effectively carry out the phase reversal protection to the motor to construct comparatively simply, the preparation, installation cost is all lower, and the installation work volume is also little, and has the universality, is suitable for popularization and application.