The present utility model relates to the technical field of engines, in particular to a low-emission cylinder with an external scavenging duct, wherein cylinder side covers are mounted on two opposite side walls of a cylinder body, a top surface of the cylinder body is a top surface of the uppermost cooling fin and a bottom surface thereof is a mounting surface, an exhaust port is provided in an inner cylinder bore of the cylinder body, an exhaust outlet is provided on a side wall of the cylinder body corresponding to the exhaust port, scavenging ports are respectively provided on two side walls in the inner cylinder bore adjacent to the exhaust port, a scavenging bore is provided in the side wall opposite to the exhaust port in an axial direction, a scavenging duct inlet is provided on the mounting surface corresponding to the side wall of the scavenging bore, scavenging grooves are respectively provided outside the side walls corresponding to the scavenging ports, and scavenging duct is formed between the corresponding scavenging port, the scavenging groove, the scavenging bore, the scavenging duct inlet and the cylinder side cover. The advantages are as follows: the low-emission cylinder can not only ensure the power performance and economical efficiency of engines, has low emission values without needing a secondary purification treatment, but can also satisfy the requirements on the limit values of emission standard.