According to one aspect of the present invention, there is provided a composting system, comprising: a composting barn having a housing structure with an open upper side, into which compost raw materials are introduced and subjected to fermentation and maturation; an ammonia concentration sensor and a hydrogen sulfide sensor installed inside the composting barn; a control device configured to receive an ammonia concentration signal and a hydrogen sulfide concentration signal from the ammonia concentration sensor and the hydrogen sulfide sensor, and to generate control signals for supplying air to the composting barn or discharging gas from the composting barn; a blower device configured to generate air pressure so as to supply air to the composting barn or draw gas from the composting barn; and a leachate storage tank configured to store gas and leachate discharged from the composting barn; wherein the control device controls the blower device in an air-supply cycle, in which air is injected into the composting barn through an air nozzle pipe when the ammonia concentration signal and the hydrogen sulfide concentration signal are within a predetermined concentration range or below, and controls the blower device in a gas-discharge cycle, in which gas is discharged from the composting barn through the air nozzle pipe when the ammonia concentration signal and the hydrogen sulfide concentration signal exceed the predetermined concentration range, thereby providing a composting system that switches the air supply mode according to the concentration of malodorous gases.