The invention discloses a full-automatic deaerator exhausting heat energy recycling method. The method includes the following steps that firstly, a full-automatic deaerator exhausting heat energy recycling system is manufactured; secondly, steam exhausted by a deaerator enters a water-steam mixer, desalted water in a slag cooling machine enters the water-steam mixer, the desalted water entering the water-steam mixer and the steam flow oppositely in opposite directions and are sufficiently mixed in a contact manner in a mixing cavity of the water-steam mixer to form a uniform water-steam mixture, and then the water-steam mixture enters a degassing water storage tank through a connecting pipeline; thirdly, the water-steam mixture is heated, degassing and deoxidizing are conducted, non-condensable gas which is separated out is discharged into the atmosphere, first-class deoxidizing and exhausting are achieved, and the water-steam mixture obtained after first-class deoxidizing and exhausting flows into a pressure bearing buffering tank; and fourthly, the non-condensable gas overflows out of the water surface of the pressure bearing buffering tank and is then discharged out, second-class deoxidizing and exhausting are achieved, and hot water flows back into the deaerator. The invention further discloses the full-automatic deaerator exhausting heat energy recycling system.