Abstract: Heterostyly is a genetically controlled floral polymorphism in which plant populations are composed of two (distyly) or three (tristyly) floral morphs. Based on the many references at home and in the world and the own works, the classification, characters, distribution and evolution of heterostylous plants were reviewed in the present paper. At present, the heterostylous plants of 193 genera, oblonging to 30 families, which account for 1%-2% flowering plants, were found. The morphs of heterostylous species differ reciprocally in the heights of stigmas and anthers in flowers, accompanied with ancillary morphological polymorphisms involving the number and size of pollen, the color and size of anther, the shape of style, the height, density, and distribution of papillae. Heterostylous plants always have physiological self- and intra- incompatibility system, but under certain circumstances, they present fertility at different level. Heterostyly seems to have evolved in different directions, one towards dioecy or subdioecy, another towards agamospermy, and the third towards homostyly and self-fertility. Heterostyly was now considered to limit functional interference between sexual organs and avoid self-pollination. Combining molecular technologies and ecological methods, wild observations and biological statistics are still the important job in the future. Studies on heterostyly could provide purviews and inspiration for plant reproduction, development and evolution, the conservation and utilization for the rare and endangerded plant resources, as well as the coevolution between plants and animals.