The invention provides a mounting method of a reciprocating compressor. A buffer tank is directly mounted on a cylinder, and in order to improve the stress condition, a longitudinal levelness value of a reciprocating compressor unit is measured; a crankshaft and a motor are centered and then linked after a compressor body and a middle body are leveled and aligned, and in order to improve the stress condition, an axial levelness value of the reciprocating compressor unit is measured. Unit leveling and aligning are performed to guarantee uniform distribution of radial clearance between a piston body and a cylinder mirror surface; otherwise, on the basis that the compressor body, the middle body, the cylinder and a piston rod are horizontal, the radial clearance between the piston body and the cylinder mirror surface is measured through a filler gauge, and if the radial clearance is uniform in distribution, the compressor body, the middle body and the cylinder meets the leveling and alignment requirements in a static state. If the center line of a crosshead and the center line of a piston are not on the same straight line, the center line, connecting the piston with the crosshead, of the piston rod has certain slope surely, and the slope ranges from a jumpiness value of the piston rod in the travel to the deviation of the length of the piston rod and the center line. The mounting method has the advantages of high mounting precision and high mounting speed.