The invention discloses a floating-up control device suitable for a quasi-rectangular shield tunnel. The device comprises a construction frame set and a counterweight frame, wherein the construction frame set is arranged at a shield tail of a quasi-rectangular shield machine in a dragging manner along a construction track in an excavated tunnel; the construction frame set comprises a plurality of construction frames connected in sequence through first connecting beams; the counterweight frame is connected to the first construction frame, closest to the shield tail of the quasi-rectangular shield machine, in the construction frames through a second connecting beam along the construction track in the excavated tunnel; and counterweight blocks are loaded on the counterweight frame by piling to ensure that anti-buoyancy force of the current excavated tunnel is not smaller than floating-up force on the tunnel. According to the device, the counterweight frame is arranged at the shield tail of the quasi-rectangular shield machine in the dragging manner and the counterweight blocks are loaded on the counterweight frame by piling, so that the weight of the current excavated tunnel is increased, the anti-buoyancy force of the tunnel is directly increased, and the anti-buoyancy force of the current excavated tunnel is not smaller than the floating-up force on the tunnel; and moreover, the quasi-rectangular shield machine and the counterweight frame can be synchronously propelled without the need for carrying the counterweight blocks for multiple times.