The invention discloses a single heat storage type steam boiler burning liquid fuel and a combustion method thereof. The steam boiler comprises a heating chamber which is internally provided with a serpentuator, combustion chambers are arranged on two sides of the heating chamber, each of the combustion chamber is provided with a combustor, an air gate of the combustor is connected with a heat storage chamber. The fuel for combustion is liquid fuel, in the process of combustion; the combustor on one combustion chamber is used for combustion, while the combustor on the other combustion chamberis used for discharging flue gas after combustion. When the combustion lasts for the preset time, the combustor in operation stops for discharging smoke and when the combustor discharging smoke stopsthe process, combustion starts. The process is periodically repeated. During the process of the smoke discharge of the flamer, the heat storage chamber absorbs the excess heat of the smoke; while in the process of burning of the combustor, the heat storage chamber releases absorbed heat to combustion air, preheating is carried out on the combustion air. By adopting the combustion method, the steam boiler of the invention ensures high thermal efficiency, low pollutant discharge and low energy consumption.