The invention discloses an adjusting device for assembly of prefabricated flange plates of a box girder and relates to the technical field of civil engineering. The adjusting device comprises a motorbracket, a fixed end template frame, a fixed end template, a guiding mechanism and a driving mechanism. A template frame slide rail is arranged at the front end of the fixed end template frame. The fixed end template is slidably connected to the template frame slide rail, and the upper end of the fixed end template is connected with a traction rope. The traction rope penetrates through the guidingmechanism to be connected to the driving mechanism to realize vertical movement of the fixed end template. The adjusting device realizes vertical position adjustment of the fixed end template by means of the driving mechanism and the guiding mechanism. The adjustment precision of the adjusting device is higher than that of a conventional support structure, and a complicated template support doesnot need to be erected. In addition, the adjusting device can be reused, thereby reducing the cost of raw materials.