The invention discloses an energy-saving and environment-friendly motorcycle engine which comprises a gas cylinder. A combustion cavity with a gas mixture is formed in the gas cylinder. A piston is insliding connection in the combustion cavity. The lower side of the piston is rotationally connected with a connecting rod. The end, away from the piston, of the connecting rod is driven by a crankshaft. Cavities are symmetrically formed in the piston. Permanent magnets are symmetrically arranged on the inner side wall of each cavity, and the magnetic poles of the opposite sides of the two permanent magnets of each cavity are opposite. Metal plates are fixedly connected to the two ends of the piston. A vertically-arranged electric heating element is mounted on the side, close to the piston, ofeach metal plate. Each cavity is transversely and rotationally connected with a rotating shaft. According to the energy-saving and environment-friendly motorcycle engine, through the interaction of the electric heating elements, rotating coils, the permanent magnets, starting plates, the rotating shafts, conveying cavities and the like, the electric heating elements can emit heat when the pistonis at the second stroke, and therefore the metal plates keep certain temperature, the situation that the gap becomes large due to piston cold shrinkage is avoided, and starting noise is lowered.