The invention provides an internal combustion engine with a plurality of firing modes. The internal combustion engine comprises a crankshaft, an auxiliary crankshaft, a connecting rod, an auxiliary connecting rod, a piston, an auxiliary piston, a cylinder and an auxiliary cylinder, wherein the top of the piston is provided with a cylindrical pit for receiving the auxiliary piston in a corresponding shape. During operation of the internal combustion engine, depending on the differences in a phase difference beta between the crankshaft and the auxiliary crankshaft, the auxiliary piston may or may not be inserted into the pit at the top of the piston; and when the phase difference beta is quite small, the auxiliary piston is inserted into the pit at the top of the piston and divides a combustion chamber into a first combustion chamber and a second combustion chamber. By changing a compression ratio, an excess air coefficient, an intake air amount and an EGR, the firing mode of the internal combustion engine can be conveniently switched between a compressed combustion mode and a compressed ignition mode, and therefore the internal combustion engine is suitable for various internal combustion engine loads.