Disclosed are a system and a method for precisely controlling an air fuel ratio of an oil burner, which is extensively used in a household boiler, an industrial boiler, or a heater, using an air pressure sensor. The system includes a power supplying part, a fan for supplying air required for combustion of the oil burner by receiving driving voltage from the power supplying part, a fan driving part serving as a controller which drives the fan, an air pressure sensor, which is installed at a side of a flow path of air supplied from the fan so as to detect an amount of the supplied air, and a contro 1 part for outputting an optimum RPM of the fan to the fan driving part by comparing a signal detected by the air pressure sensor with preset data related to an optimum amount of air. The method includes the steps of detecting an amount of air being supplied through a fan using the air pressure sensor, calculating an optimum RPM of the fan using a controller by comparing a signal about the amount of the air with preset data related to an optimum amount of air, outputting the RPM calculated by means of the controller to a fan driving part, and rotating the fan according to the calculated RPM input into the fan driving part.