The invention relates to the technical field of common small type two-stroke engines, in particular to a two-stroke engine cylinder block lengthened type closed scavenging passage. A mixed gas storage cavity is formed below a cylinder block exhaust port and communicated with a crankshaft case, a cylinder block scavenging way is divided by a separating wall on a side cover into two independent scavenging ways, and the two scavenging ways are communicated to the mixed gas storage cavity and the crankshaft case correspondingly; and a groove channel is designed in a flange face of a cylinder block so as to communicate the mixed gas storage cavity and another closed scavenging way. The flange face of the cylinder block is matched with a thin plate where a through hole is designed, so that mixed gas passes through the mixed gas storage cavity, the channel and the closed scavenging way to enter the cylinder block, the side of the exhaust port is cooled, and the length of the closed scavenging way is increased. Through increase of the length of the closed scavenging way, layering of pure air and mixed gas is facilitated, the pure air guide tail gas scavenging stability is improved, the power of an engine can be effectively improved, the high-low speed stability can be effectively improved, and tail gas emission is reduced.