The invention provides a dual-fuel sparking plug type four-stroke engine based on reformed gas and a combustion control method, and belongs to the field of internal combustion engine combustion. A cylinder cover is provided with an in-cylinder direct-injection first fuel nozzle and/or a gas inlet channel is provided with a gas inlet channel first fuel nozzle, and the cylinder cover is provided with an in-cylinder direct-injection second fuel nozzle and/or the gas inlet channel is provided with a gas inlet channel second fuel nozzle; the cylinder cover is provided with a sparking plug; and thecylinder cover and/or the gas inlet channel is provided with a reformed gas nozzle. In the state that main fuel nozzles are simultaneously installed on the cylinder cover and the gas inlet channel, when the engine is in low load, fuel is supplied by the cylinder cover main fuel nozzle, and the heat efficiency is improved; when the engine is in middle load, the fuel is supplied by the gas inlet channel main fuel nozzle, and generation of NOx is reduced; and when the engine is in high load, the fuel is supplied by the gas inlet channel nozzle and the cylinder cover nozzle of main fuel, and knocking is controlled. Efficient and clean combustion in all working condition ranges is achieved.