According to the problem of soybean lodging in production, three levels of potassium application rates were designed to compare the lodging-resistance characters of soybean stem. The results showed that the potassium regulation increased the stem lodging- resistance ability of soybean. Application of potassium fertilizer made the length of first to fifth internodes from basal shortened, diameter increased and position of maximum diameter of internodes shifted down. Compared with no application of potassium fertilizer,potassium regulation made the plant centre of gravity height descended, the fresh weight of basal internodes and the fresh weight of unit length of internodes increased. At the same time, the stem crushing strength of each node, stem bending capacity and the stem lodging-resistance ability were all improved. The lodging degree in different potassium fertilizer treatment was: low potassium ＞ high potassium ＞ middle potassium.