A system for managing a seat occupancy status by a passenger and a control method of the system includes a seat belt sensor provided for each seat to detect a fastening or unfastening of the seat belt, a pressure detection unit provided for each seat to detect occupancy or non-occupancy of a seat by a passenger and pressure of the seated passenger, a secondary control unit provided for each seat and woken up by radio communication with a vehicle to alert to an unfastened state of the seat belt when the seat belt is unfastened upon determining, by a seat belt sensor, whether the seat belt is fastened, and a primary control unit provided in the vehicle to perform radio communications with each secondary control unit and check an abnormality based on reception or non-reception of the system data transmitted from the secondary control unit.