The invention discloses a liquid nitrogen gasifying device for combustible gas or combustible liquid pipe purging. The device comprises a frame, and a liquid nitrogen storage tank, a pipeline system,a low-temperature plunger pump, a gasifying machine, a fan, a diesel generator and the like mounted in the frame; the diesel generator guarantees supply of electric power to the device under powerlessenvironment; the pipeline system comprises a gas-phase pipeline, a liquid inlet/outlet pipeline and a nitrogen outlet pipe; the low-temperature plunger pump extracts liquid nitrogen from the liquid nitrogen storage tank, and sends the liquid nitrogen into the gasifying machine by the liquid inlet/outlet pipeline; the gasifying machine is in an empty bath form; the fan intensifies the heat exchange effect; and gasified nitrogen is output for pipe purging after being heated by a resistance heating strip wound on the nitrogen outlet pipe. The device integrates such functions as storage, gasification, heating and control of the liquid nitrogen, is compact in structure, can be placed on a motor vehicle, is convenient to transport and apply, meets the requirement of high use level of purging nitrogen, and can be used under powerless environment.