The invention discloses a crankcase having a compressed air buffering function. The crankcase having the compressed air buffering function is used for installing a crank shaft on a piston type air compressor. The crankcase is provided with a top face, wherein the top face and the bottom face of an air cylinder are sealed. The top face is provided with a piston opening. The piston opening is used for communicating with an air cylinder piston cavity, so that a connection rod is made to be connected with a piston in a piston cavity of the air cylinder and the crankshaft installed in the crankcase. The top of the crankcase is provided with a crankcase annular channel. The crankcase annular channel surrounds the piston opening. The top face of the crankcase is provided with an upward annular opening. The crankcase annular channel is used for compressed air buffering. The annular opening is used for butt joint with an annular air channel on the bottom face of the air cylinder. The side face of the crankcase is provided with a water collection tank. An inclined and downward water collection channel is arranged on the side edge of the crankcase. The water collection channel communicates with the water collection tank and the crankcase annular channel.