The climate, vegetation, soils, and farming are obviously different between subhumid and semiarid areas. For a long time, because of the difference of principles, methods, and indexes, there is divergence about the boundary line. The indexes, which have been used in physico-geographical regionalization in China, have been compared. We can see that the aridity or humidity indexes, aerial relative humidity, vegetation, soil and its sectional texture, and crops had been used as the major indexes. The formula, calculating the aridity or the humidity indexes, is based on experience. The formulas computing the potential evaporation are different. At the same time, the data comes from a year, so they can not comprehensively mirror the seasonal change of aridity and humidity. The real moisture condition can not be reflected either. The aridity and humidity of a region should be measured on the basis of moisture balance. But its function in regionalization was limited owing to some components and parameters. In views of the above-mentioned facts, the author put forward the indexes, which should be considered emphatically when a boundary line between subhumid and semiarid sectors is delimited. According to some principles and methods, it will be the prerequisite for the demarcation between subhumid and semiarid sectors to integrate the comprehensive and the dominant factors, and select the indexes well.