The physical essence of the hypothesis of layerwise intermixing and its utilization for the calculation of the gas exchange processes in the cylinder of a two-stroke engine are presented. A system of equations is obtained which permits calculation of the parameters in the cylinder during scavenging. The effect of different design and operational factors, such as the gas distribution phases, the rate of revolution of the engine shaft, the supercharging pressure, etc. on the quality of gas exchange processes can be analyzed theoretically.