The invention relates to a medium-caliber 9Ni low-temperature seamless steel tube and a production method. The seamless steel tube comprises, by mass, less than or equal to 0.06% of C, 0.13%-0.28% of Si, 0.40%-0.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 8.7%-9.30% of Ni, 0.03%-0.07% of Mo, 0.01%-0.040% of Al and the balanced Fe and inevitable impurities. The seamless steel tube is produced through an MPM retained mandrel tandem rolling process. The production method includes the steps of tube blank inspection, tube blank discharging, circular furnace heating, tapered roller puncher punching, borax blowing, tube rolling through an MPM retained mandrel tandem rolling machine, working of an extracting mill, reheating through a stepping furnace, high pressure water descaling, diameter determining, cooling through a cooling bed, saw cutting through a pipe saw mill, straightening, leakage flux flaw detection, manual inspection and coping, heat processing, straightening, coping processing on the inner surface and the outer surface of a steel tube, ultrasonic flaw detection, manual reinspection, cleaning, identifying, packaging and storage.