The invention discloses a two-stroke internal combustion engine which solves the problems that in the work process of a two-stroke internal combustion engine, some non-combusted scavenging gas can break away from an exhaust port so as to flow into the atmosphere, which will result in pollution and lowering of the combustion efficiency. According to the technical scheme of the two-stroke internal combustion engine, the two-stroke internal combustion engine is characterized in that a first scavenging port of a first-stage scavenging channel is higher than a second scavenging port of a second-stage scavenging channel; the two-stroke internal combustion engine further comprises a plurality of auxiliary gas inlet channels communicating a combustion chamber with a crankcase; and auxiliary gas inlets of the auxiliary gas inlet channels are located below the first scavenging port. It is achieved that non-combusted gasoline mixed gas in tail gas exhausting is effectively reduced, and the scavenging efficiency can be improved.