:This paper analyzed and studied the in-cylinder flow in two engines. Both are two-stroke loop scavenging 8-cylinder in-line engines. One cylinder diameter is 150mm and the other is 160mm. For researching its loop scavenging performance, one cylinder of both engines is examined. The upper section of the cylinder above the ports is cut off and replaced by a glass one, and the cylinder head is replaced by a plexiglass plate. Then they are mounted on the test bench. A metal screen is put in the glass cylinders. Threads are tied at the screen cross points. The direction of flow in cylinder can be visualized when the air flows. A kind of instrument, named Hot Ball Anemometer, is applied to measure the air flowing speed. The diesel's loop scavenging performance can be realized and satisfactory results obtained.