Abstract: A multi-fuel pre-mixed combustion system of an internal combustion engine includes a main fuel spray nozzle (2), which injects a mixed fuel of compression-ignition-suitable fuels, spark-ignition-suitable fuel, or a wide cut fuel to form a homogeneous primary pre-mixed gas. An auxiliary spray nozzle (4) injects a spark-ignition-suitable fuel to form a secondary mixed gas, which is ignited by the spark plug (3) by means of spray guiding or an ignition chamber (5), and the primary pre-mixed gas in the combustion chamber (1) is compression ignited. Consequently, the ignition point of the primary mixed gas is effectively controlled and knock is avoided, and a homogeneous pre-mixed compression ignition is achieved over the whole range of operating conditions. The combustion rate is controlled by exhaust gas recirculation or spray of water into a cylinder or intake port, and high thermal efficiency is ensured by a high expansion ratio.