The invention discloses a welding process of a plunger assembly of a hydraulic buffer. The welding process comprises the following steps that firstly, a bottom plate and a base are correspondingly arranged in a left end hole and a right end hole of a plunger one to one, so that a plunger assembly to be welded is formed; secondly, the plunger assembly to be welded is placed on an auxiliary support of a welding tool, then the height of the auxiliary support is adjusted, a right-end ejector pin abuts against a central hole of a base plate, and a left-end ejector pin abuts against a central hole of the bottom plate; thirdly, a welding control button is started, a welding nozzle of a welder is made to get close to the welding position, at the left end, of the bottom plate and the plunger first, arc starting is conducted, meanwhile a servo motor on the welding tool drives the plunger assembly to rotate, welding is conducted in a circle, a robot is made to turn around, the welding nozzle of the welder is made to get close to the right end, and the welding position of the base plate and the plunger is welded automatically. According to the welding process, clamping time and welding time can be shortened, welding performance is stable, welding quality is high, and work efficiency is high.