The invention relates to a combustion control method of a gas water heater. The gas water heater comprises a combustor, a proportional valve, a fan and a controller, and is characterized in that a wind pressure sensor is arranged at an exhaust port of the gas water heater, the wind pressure sensor is also connected with the controller, and a wind pressure reference database and a fan rotation speed compensation database are preset and stored in the controller. Compared with the prior art, the method has the advantages that when external wind pressure does not exist, detection values of the fanat different rotating speeds through the wind pressure sensor are stored in advance as wind pressure reference values, the rotating speed compensation amount required of the fan at different reference rotating speed conditions and different wind pressure values existing outside is stored in advance as well, so that the influence of wind pressure generated by the fan on the detection value of thewind pressure sensor can be well avoided, and meanwhile, adjustment on the rotating speed of the fan is accurately controlled, and the control method is more accurate.