Abstract: Our research has clearly confirmed distyly in Polygonum orientale. Long-styled and short-styled morph exhibited a precise reciprocal herkogamy which was significantly correlated with corolla length. Research showed that anther heights, tepals, stigma and pollen size and number were dimorphic (P<0.01). Compared with the pins, the thrums had larger tepals and the stigma had more but shorter papillae. The anther produced significantly bigger but fewer pollen grains. There was no significant difference between long-styled and short-styled in terms of tepal length (P>0.01). In terms of micro-morphological characteristics, pollen grains were spherical or sub-orbicular, with irregular margins and scattered holes. Thrips, ants and flower flies were the main visitors to the flowers. Artificial pollination revealed that pollen tube shape was normal in both morphs, with the tubes reaching the ovary 0.5 h after pollination. Not all pollen tubes growing down the stylar canal and ovary wall were able to reach the ovary, indicating the existence of chalazogamy in P. orientale.Long-styled and short-styled intramorph fruit sets were 14.00% and 13.33% respectively. Self-pollination fruit sets were 4.62% and 2.86% and intermorph fruit sets were 43.33% and 44.61% respectively. Self-pollination showed some affinity, but the fruit sets were low and the flowers were still predominantly intermorph.