A multiple hydraulic robot system for precisely installing a girder according to the present disclosure may comprise: four hydraulic robots connected to both sides of two connection plates which are coupled to both ends of the top surface of a girder installed between bridge piers and to which cables of a crane are connected, wherein the robots move the girder horizontally and vertically; a hydraulic system for operating actuators of the four hydraulic robots; and a controller which controls the remotely operated four hydraulic robots by means of a synchronization control algorithm to precisely adjust the installing position of the girder.