The embodiments of the present application disclose a combustion control system of a gas water heater or wall-hanging boiler, and a control method thereof. The system comprises: a flue gas channel consisted of a combustor, a heat exchanger and a stepless speed regulating fan and a smoke tube, which are connected sequentially; a control unit connected to a signal input end of the stepless speed regulating fan; a wind pressure sensor assembly that detects a pressure signal upstream of an impeller of the stepless speed regulating fan, a signal output end of the wind pressure sensor assembly being connected to the control unit; the control unit comprising a storage for storing a correspondence relationship between the pressure signal upstream of the stepless speed regulating fan and a thermal load of the combustor, and a controller that controls operation of the stepless speed regulating fan according to the correspondence relationship. The present application further regulates the rotational speed of the stepless speed regulating fan by detecting the pressure signal upstream of the impeller of the stepless speed regulating fan, thereby achieving a better wind-resistant performance of the present application.