The invention discloses a water heating system based on multistage combustion. The water heating system comprises water heating equipment, a cold water inlet pipe and a hot water outlet pipe; the water outlet end of the cold water inlet pipe communicates with the cold water inlet end of the water heating equipment; and the hot water outlet end of the water heating equipment communicates with the hot water outlet pipe. By adopting two air preheating devices, flue gas waste heat obtained after combustion is fully utilized, combustion-supporting air which is about to enter a combustion device isfully preheated, and the heat utilization rate of the whole equipment is effectively increased.