The invention discloses an automobile rear axle housing flange plate press-fitting welding device which is used for solving the problems of being multiple in procedure, low in mounting efficiency, incapable of guaranteeing welding precision of flange plates and the like in an existing automobile rear axle housing flange plate press-fitting process. The automobile rear axle housing flange plate press-fitting welding device comprises a combined lathe bed, welding mechanisms and a clamping mechanism. According to the technical characteristics, the combined lathe bed is composed of a main body lathe bed and side lathe beds, wherein the middle of the upper surface of the main body lathe bed is provided with a lifting clamping mechanism used for limiting and smoothing a rear axle housing; rotating mechanisms with adjustable feeding strokes comprise hydraulic feeding units and rotary driving units, and the welding mechanisms are arranged on the upper surfaces of the side lathe beds; and the clamping mechanism comprises a self-centering clamping mechanism and the lifting clamping mechanism, and the lifting clamping mechanism is adjusted to enable the axes of flange plates and the axis of an axle housing pipe to be located on the same central line. According to the automobile rear axle housing flange plate press-fitting welding device, the structural design is reasonable, the technological process is simplified, assembling and positioning are accurate, welding deformation is easy to control, while precision of the mounting surfaces of the flange plates is ensured, the machining costis reasonably reduced, the quality and production efficiency of a finished product are improved, and therefore driving safety is guaranteed.