A vehicle-mounted oxygen supply device is characterized in that: the vehicle-mounted oxygen supply device is composed of a gas generator, an air bag, and an air guiding device, and the gas generator is composed of a container, a medicament, a water storage device, a switch, and a one-way valve Composition, the air guiding device is composed of a one-way valve, a catheter, and a breathing switch. When the vehicle falls into the water, the gas supply switch in the gas generator is turned on, and the internal reaction occurs to generate oxygen. The gas enters the airbag through the one-way valve, and the occupants of the vehicle can inhale oxygen through the breathing port, and at the same time, the exhaled gas passes through the one-way valve through the breathing port. And the guide of the catheter enters the gas generator, the carbon dioxide in the exhaled gas in the gas generator is absorbed by the medicine inside the generator, and the remaining oxygen enters the airbag and can be used again; when the occupants are trapped in the car, the device Oxygen can be provided to ensure that it will not drown. When the occupants of the vehicle can escape from the vehicle that fell into the water, the airbag can be used as a lifebuoy to provide sufficient buoyancy for the occupants.