The present disclosure relates to a riding system of a robot which supports a PUI through user authentication to provide convenience to users, and including a server for exchanging authentication information with the robot; a mobile terminal including an application interlocking with the server and for arranging use information of the user through the application and for calling the robot through the application; and a robot storing the authentication information, to authenticate the user through the authentication information when there is a call from the mobile terminal, and deforming according to a body size of the user included in the use information and to allow the user to ride thereon and to move the user to the destination, and a control method thereof.