The invention discloses a liquid slag buffer storage device with heat compensating and preheating functions. The device comprises a slag ladle shell, a fixed-diameter water nozzle, a plug bar, a combustor, a seal cover, a slag falling pipe, a waste heat recycling module and a chimney; a slag inlet is formed in the top of the slag ladle shell, a slag outlet is formed in the bottom of the slag ladleshell, the combustor is arranged on the upper or the side of the slag ladle shell, the top of the slag ladle shell is of an arch structure built through refractory bricks, the thickness ratio of theladle bottom material to the side wall material of the slag ladle shell is 1.4-2.2, the fixed-diameter water nozzle and the plug bar matched with the fixed-diameter water nozzle are arranged on the slag outlet, the seal cover is arranged on the slag outlet, the slag falling pipe is arranged on the bottom of the seal cover, a granulating chamber is arranged on the lower portion of the slag fallingpipe, and is the waste heat recycling module, and an outlet of the waste heat recycling module communicates with the chimney. Ladle baking, heat compensating, preheating, seal, flow control, and slagladle top fireproof material and combustor falling prevention functions during system running can be achieved, and the device can be widely applied to liquid-state slag granulation waste heat recycling systems.