The present invention provides a heating device of a drinking fountain in a car. It has a helical pipe, a wire net, an iron container, fireproof mud and a car exhaust pipe. The helical pipe is installed outside the car exhaust pipe and the wire net is used to cover the pipes. The iron container covers the wire net, the helical pipe and the car exhaust pipe. Fireproof mud is poured into the reserved space in the iron container and it is sealed completely. One end of the helical pipe is a water outlet, while the other end is a water intake. The car exhaust pipe generates high temperature and heats the helical pipe which is insulated by fireproof mud. When users push the drinking fountain switch, a motor will operate to pump out water from water storage. The water is heated when it goes by the helical pipe.