The present invention belongs to the field of communication and particularly provides a seat reserving method and system for an ordering system. The method comprises: 101, receiving a reservation application of a user, wherein the application comprises a reservation mobile phone number, reservation time and a reservation people number; 102, when reaching the seat reservation time, acquiring position information of the reservation mobile phone number; and 103, calculating a distance between the position information and position information of a restaurant, directly canceling the reservation if the distance is greater than a set threshold value, or retaining the reservation and sending a prompt short message to the reservation mobile phone number. According to the technical scheme provided by the present invention, the seat reserving method and system for the ordering system have the advantage of saving seat resources.