800CC engine system has four-stroke, double cylinders and eight-valve, overhead camshaft, water-cooled engine and independent transmission. The structure is complex. Aviation technology is adopted. Technical content is high. Both structure design and process design all represents the most advanced design level of all-terrain vehicle engine at present; for instance, it has eight-valve bidirectional symmetric combustion chamber, lightweight piston, rotary automatic tensioner; damping and automatic braking CVT system can change gear in any condition. In addition, the vehicle can enter decelerating braking state automatically when it travels downhill. In this way, driving becomes safer; top domestic DELPH multiple-point electric control system makes power performance of the engine become much better. It is much greener and more environmentally-friendly; independent transmission structure makes maintenance become more convenient and quick; cylinder plateau honing process and whole crankshaft N conversion + mirror light technology make durability of the engine improved greatly.