The invention discloses a device for cyclic dewfall air-return adjustment of a large low-temperature liquid cargo ship. The device comprises a cargo cabin air return header pipe and a dry isolation cabin air return header pipe which are connected to an emptying hole of a cargo cabin/dry isolation cabin, wherein the cargo cabin air return header pipe and the dry isolation cabin air return header pipe are connected to a balance valve; one outlet of the balance value is successively connected to a venturi tube, an air filter and a pressure balance tank; two air outlets of the pressure balance tank are connected to an escape pipe and an inlet end of an original drying dewfall device of the ship; a water outlet of the air filter is connected to a condensed water drainage pipeline; an air supplementation hole of the venturi tube is connected to a new air pipe; and another outlet of the balance value is connected to the escape pipe. According to the invention, the cabin-charging discharge gas which has a certain pressure and is treated by drying and dewfall is used repeatedly; equipment such as the venturi tube is used to generate effects of temperature decrease, pressure decrease and negative-pressure absorption; and the gas is mixed with the supplemented air, and pressure adjustment is conducted then, so that a gas dew point at the inlet of the original drying dewfall device of the ship can be reduce cyclically and continuously.