The present disclosure relates to a control method of a gas furnace comprising a step for measuring an indoor temperature, a step for comparing the indoor temperature with a set temperature for heating, and a step for operating the gas furnace in weak heating with a predetermined heating capacity which is lower than a maximum heating capacity of the gas furnace, when the set temperature for heating is higher than the indoor temperature by a temperature value which is less than a predetermined temperature value, wherein the predetermined heating capacity for weak heating is maintained at a current heating capacity for weak heating, when the gas furnace operates in weak heating, and when an operating duration with the current heating capacity for weak heating is less than a first time value.