The invention provides an automatic pin shaft assembling machine. The automatic pin shaft assembling machine comprises a main base (24). The bottom of the main base (24) is provided with a sliding wheel (26). One side of the main base (24) is provided with an electric control box (23). The other side of the main base (24) is provided with a piece discharge plate (25). A working platform (32) is arranged on the main base (24). The bottom of the working platform (32) is provided with a seventh air cylinder (20) and a rotating disc (21) which are arranged side by side. An assembling piece clamp (19) is arranged above the rotating disc (21). A pin shaft assembling clamp (15) is arranged above the assembling piece clamp (19). An assembly push rod (14) is arranged above the pin shaft assembling clamp (15). The top of the working platform (32) is provided with a control valve (2) and a vibration disc (1). A pin shaft pipe (3) is arranged in the vibration disc (1) and extends downwards to the top of the pin shaft assembling clamp (15). The automatic pin shaft assembling machine has the advantages that working efficiency is improved, the manual cost is saved, mounting accuracy is improved, and thus production benefits are increased greatly.