The invention relates to a combustion control method of a gas water heater. The gas water heater comprises a first electromagnetic proportional valve, a second electromagnetic proportional valve, a draught fan, an igniter, a combustor and a main valve, wherein the first electromagnetic proportional valve and the second electromagnetic proportional valve are used for adjusting the combustion parameters. The gas water heater has three work modes including a one-section work mode, a two-section work mode and a three-section work mode. The three work modes have corresponding combustion parameters. In the one-section work mode, the first electromagnetic proportional valve is switched on, in the two-section work mode, the second electromagnetic proportional valve is switched on, and in the three-section work mode, the first electromagnetic valve and the second electromagnetic valve are both switched on. The combustion control method of the gas water heater is characterized in that when the one-section work mode and the two-section work mode is switched, the three-section work mode is executed for 300-800 ms first of all, and then switching is conducted. Compared with the prior art, the combustion control method of the gas water heater has the advantage of being capable of greatly improving the success rate of flame spreading.