The invention relates to a mounting structure of a bottom fork and a rear axle shell of a four-wheel motorcycle. The rear axle shell is arranged in a bottom fork anchor ear; the outer wall at one end of the rear axle shell is provided with a locating boss for locating one end surface of the bottom fork anchor ear, the other end of the rear axle shell is sleeved with a rear disk brake support which is tightly clamped on the other end surface of the bottom fork anchor ear through a clamp spring I, and the other end of the rear disk brake support is sleeved on a rear disk brake locating column arranged on a bottom fork side pipe at the opposite side. A circular groove is arranged in the rear disk brake locating column and is internally provided with a clamp spring II which tightly clamps theother end of the rear disk brake support, and a wavelike elastic gasket is arranged between the clamp spring II and the other end of the rear disk brake support. The bottom fork is located on the rear axle shell through a limiting boss and the clamp springs more easily; meanwhile, the mounting precision of a locking support lug is lowered. The bottom fork anchor ear is machined from a round steelpipe, has little deformation and is beneficial to being mounted together with the rear axle shell.