To investigate the differences in flower bud differentiation and anther development between male sterile and fertile materials of ramie, male steril ramie including male flower atrophic type (Yuanqing No.5), male flower indehiscent type (Wanzi ramie), pollen sterility type (Huangxiaoyie) and fertile ramie Zhong Zhu No.1 (control) were selected to compare the development of male flower buds by paraffin section technology. The results showed that flower buds of male steril ramie develop faster than Zhongzhu No.1. When the flower buds are 0.30.5 cm long, the differentiation of pistil and stamen are completed. It is speculated according to the differentiation of flower buds and anther development of Zhong Zhu No.1 that the cause of male steril for Yuanqing No.5 was after differentiation of anther and filament, anther wouldn’t differentiate to form pollen sac, but undergo atrophy, or even disappear and form cavity; for Wanzi Ramie, the cause was serious lignified perianth in the stage of pollen differentiation, for huangxiaoyie the unruptured pollen sac, abnormal intumescence of filament and the darkened colour of pollen grain.