The invention discloses an integrally-suspended gravitational levelling type laser measuring instrument for a building. The instrument comprises a main instrument frame, wherein gear racks which are matched with gears through a gear shaft are arranged at two sides of the upper part of the main instrument frame; a group of movable transverse racks is arranged in the main instrument frame in a sliding manner; sliding racks which are engaged with the gears are arranged at the upper parts of the movable transverse racks; the end parts of the movable transverse racks are connected with side frames which are in match with lifting oil cylinders; a slide seat is arranged at the lower part of the main instrument rack in a sliding manner, and a connecting rod is arranged at the lower part of the slide seat; an angle ruler is arranged at the lower part of the connecting rod, and the bottom end of the connecting rod is in rotating fitting with a main machine of the measuring instrument. According to the integrally-suspended gravitational levelling type laser measuring instrument for the building, the span and the height can be flexibly adjusted; meanwhile, the levelness of the main machine of the measuring instrument can be ensured, and the main machine of the measuring instrument be accurately transversely moved and rotated by angles during being operated, so that the building measurement accuracy can be ensured.