The invention relates to the technical field of internal combustion engines and discloses an engine ignition mechanism. The engine ignition mechanism comprises a spark plug and a flame accelerating cavity. The flame accelerating cavity is arranged in a cylinder cover. The spark plug extends into one end of the flame accelerating cavity. The other end of the flame accelerating cavity communicates with a main combustion chamber. Annular spoilers are arranged in the flame accelerating cavity. The invention further discloses an engine combustion system comprising the cylinder cover portion and a cylinder body portion. The cylinder cover portion comprises the engine ignition mechanism, an intake valve and an exhaust valve. The cylinder body portion comprises a cylinder sleeve, a piston and a crank-link mechanism. A main combustion chamber is defined by the bottom face of the cylinder cover, the cylinder sleeve and the piston. The intake valve and the exhaust valve are connected with the main combustion chamber. According to the engine ignition mechanism, the flame accelerating cavity provided with the multiple annular spoilers is arranged between the spark plug and the main combustion chamber, the combustion process in the main combustion chamber is greatly accelerated, the combustion constant-volume degree is high, the heat efficiency is high, and besides the engine ignition mechanism is simple in design structure, low in cost and high in practicability.