Abstract: After being expanded by microwave, the expansion characteristics of the tobacco stems from the typical tobacco-growing areas in Yunnan were tested. The differences of stem's expansion characteristics and their influencing factors were studied with histogram, variance analysis and cluster analysis. The results showed that:1) The expansion characteristics of tobacco stems differed between growing areas, tobacco varieties and stalk positions. 2) The stems from Kunming featured better expansion characteristics, which could be used as the major material to produce stem granules. 3) The effects of growing area, tobacco variety, stalk position and their interactions on stem expansion characteristics reached extremely significant level (P <0.01). The interaction of the 3 factors and that of tobacco variety and stalk position impacted greater influences than did each single factor, growing area impacted greater influences than did tobacco variety and stalk position. 4) Cluster analysis indicated that stem samples could be clustered into 3 categories according to expansion rate, i.e. categories of high, moderate and low expansion rates, although the rule of sample classification affected by interaction was not obvious.