Aiming at the research of interlayer interference law in multi-layer commingled production of medium and light oil reservoirs in the south of BohaiSea, a physical model of sand filling pipe for multi-layer commingled production is established to simulate the process of multi-layer commingled production with different permeability grades and different crude oil viscosity. Based on the results of physical simulation experiment, the concepts of liquid production grade difference and interlayer interference coefficient are proposed, and the limits and timing of separate production are determined, which can guide the actual production of oil fields International development. The results show that the permeability grade difference of separate production limit of medium light oil reservoir is 4, and the time of separate production is about 80% water cut. With the increase of formation crude oil viscosity, the time of liquid extraction should be appropriately advanced. The practical application in Bohaia oilfield shows that the prediction result is close to the actual test result, and the average error is 8.75%. The field application effect is obvious, which has certain guiding significance for the follow-up oilfield field practice.