The invention relates to a lifesaving airbag for an automobile falling into water. The lifesaving airbag comprises a shell, a liquid storage chamber, a reaction chamber, an air bag, a large spring, alarge piston, mixed liquid, a small piston, an ejector rod and a blocking rod; the liquid storage chamber is communicated with the reaction chamber through a first connecting pipe; the reaction chamber is communicated with the air bag through a second connecting pipe, a flow guide pipe is arranged in the reaction chamber and placed in the reaction chamber, one end of the flow guide pipe is connected with the first connecting pipe, the other end of the flow guide pipe is closed, a certain number of small holes are formed in the flow guide pipe, and sodium peroxide and manganese dioxide powder are contained in a cavity between the reaction chamber and the flow guide pipe; the front section of the breathing tube is inserted into the air bag, a protective sleeve is connected to the breathing tube, and latticed air holes are formed in the outer end face of the protective sleeve. According to the lifesaving air bag for the automobile falling into water, after the automobile falls into water,the air bag provides oxygen for people falling into water, meanwhile, the air bag provides buoyancy for people falling into water, and the two problems that people escape and swim ashore in an existing falling-into-water accident are solved.