Abstract: Mechanical strength of inflorescence stems within seventy\|six herbaceous peony（Paeonia lactiflora Pall.） varieties were measured by mechanical strength tester determinator of plant stem， and the varieties were divided into three categories by stem mechanical strength using the method of dynamic clustering in this study， namely high mechanical strength， medium mechanical strength and low mechanical strength， and the variation range of the categories was11.9～21.3，8.5～14.2，2.8～9.7 N， respectively， the number was 14，40，22， respectively， conforming to normal distribution. The difference in stem diameter and stem weight were extremely significant among each type. The difference in flower weight was significant， but the difference in stem length was not significant. Correlation analysis showed that the stem mechanical strength was significantly positive correlated with stem diameter and stem weight， and the flower weight of low mechanical strength cultivars was significantly negative correlated with the stem mechanical strength.

Key words: herbaceous peony, inflorescence stem, mechanical strength