According to the motors working principle, the authors design and complet an electronic fuel injection system based the monolithic processor of MC68HC08. Then the authors complete a matching experiment of single-plunger fourstroke engine CG125 applying this system to the trestle. As the system used, fairly well has been settled the contradiction among the driving force of engine, the economization of fuel consumption and the letting of exhaust gas. After the testing, the power of motorcycle engine has increased about 10%, the oil consumption has decreased about 15 %, and the exhaust gas has decreased about 20%,