The invention discloses an automatic clutch gear shifting arm assembly, an engine and a motorcycle. The automatic clutch gear shifting arm assembly comprises a gear shifting shaft, a limiting plate, a moving plate, a clutch operating arm and a return torsional spring used for enabling the gear shifting shaft to return, and further comprises a guide part rotatably sleeving the gear shifting shaft, wherein the moving plate movably sleeves the gear shifting shaft and axially presses the limiting plate fixed to the gear shifting shaft under the action of elastic force; the clutch operating arm is fixedly arranged on the gear shifting shaft in the circumferential direction; the gear shifting shaft drives the moving plate to achieve gear shifting through rotational hysteresis with the clutch operating arm; and the guide part performs sliding guiding on the moving plate in the axial direction. According to the automatic clutch gear shifting arm assembly, a gear shifting moving block stably slides in a reciprocating manner in the axial direction through the guide part, reliability of motion of the moving block is improved, automatic clutch gear shifting is smooth, and the structure is simple and compact.