The invention belongs to the technical field of seawater desalination, and relates to an 'outside-cylinder parallel-connection type' non-condensable gas removing device in a low-temperature multiple-effect distillation seawater desalination system. The low-temperature multi-effect distillation seawater desalination system comprises a multiple-effect evaporator, a steam injector, a steam condenser, the 'outside-cylinder parallel-connection type' non-condensable gas removing device, a concentrated saltwater heat exchanger, a fresh water heat exchanger, a seawater material feeding pump, a concentrated saltwater pump and a fresh water pump, wherein, the 'outside-cylinder parallel-connection type' non-condensable gas removing device comprises non-condensable gas extraction pipes respectively arranged a heating steam side of each effect evaporator and outside a cylinder body of the steam condenser, valves arranged on the non-condensable gas extraction pipes, a main pipe and a vacuum pumping device; the non-condensable gas extraction pipes are connected in parallel to the main pipe; a high pressure end of the main pipe is connected with the non-condensable gas extraction pipes; and a low pressure end of the main pipe is connected with the vacuum pumping equipment. The low-temperature multiple-effect distillation seawater desalination system disclosed by the utility model can avoid or reduce the accumulation of non-condensable gas on the inner wall of a heat exchange pipe, improve the heat exchange efficiency of the multiple-effect evaporator, and ensures that a reasonable pressure difference is formed among the effect evaporators at the inner parts of the multiple-effect evaporator meanwhile.