The invention discloses an ultrahigh-pressure hydrostatic extrusion forming technology of a magnesium alloy pipe. The ultrahigh-pressure hydrostatic extrusion forming technology of the magnesium alloy pipe comprises the following steps: pressing one end of a magnesium alloy blank according to the required size of a pipe, and coating the end surface of the blank with lubricating grease or lubricating oil; putting the processed blank into an outer mold of an extrusion mold to be fixed, and installing a mold core and a mold base; performing butt joint between an extrusion cylinder and one end of the mold, wherein the end of the mold is filled with the blank and is provided with a sealing system, the other end of the extrusion cylinder is provided with an extrusion shaft; sleeving the extrusion cylinder with a heater; filling the extrusion cylinder with a liquid high-pressure medium, and exhausting air in the extrusion cylinder completely; electrifying the heater, and controlling the heating temperature to be within room temperature being 300 DEG C, and performing heat preservation for 1-3 hours; pushing the extrusion shaft to compress the high-pressure medium, and generating ultrahigh pressure being more than 300MPa, and extruding the magnesium alloy blank out, so as to obtain the pipe after passing a sizing band of the extrusion mold. The ultrahigh-pressure hydrostatic extrusion formation and the expansion and contraction formation of the magnesium alloy pipe are realized; the ultrahigh-pressure hydrostatic extrusion forming mold of the magnesium alloy pipe is developed.