The utility model discloses a phase break protection device used for a railway vehicle emergency inverter. The phase break protection device comprises a phase brake detection circuit, a reference voltage circuit, a signal conditioning circuit, a charge and discharge comparison output circuit and a DSP. When a three-phase power supply normally supplies power, the phase break detection circuit outputs a low level to be compared with the reference voltage of the reference voltage circuit, the charge and discharge comparison output circuit is made to output a high level to the DSP by enabling the signal conditioning circuit to output a low level, the DSP judges that the three-phase power supply works normally, and the fault protection action is not conducted. When phase break happens to the three-phase power supply, the phase break detection circuit outputs discontinuous half cycle sine waves to be compared with the reference voltage of the reference voltages circuit, impulse waves with a certain duty ratio are output through the signal conditioning circuit, the charge and discharge comparison output circuit is made to output a low level to the DSP, the DSP judges that the phase break happens to the three-phase power supply, and the fault protection action is not conducted. The phase break protection device is reliable in performance and can well protect devices.