The flowering biological characteristics including flowering forest appearance, floral dynamic, floral organs structure, fruit morphology and regeneration pattern of Oligostachyum spongiosum were observed by the filed investigation and optical microscopy. The process of megasporogenesis and microsporogenesis and the development of female and male gametophyte of O. spongiosum were analyzed by paraffin section and light microscope techniques. The results are as follows: (1) O. spongiosum was a massive synchronized flowering bamboo species, and its flowering period was from late April to late May. (2) The inflorescence type of O. spongiosum was paniculate mixed inflorescences. Each inflorescence consisted of 4 spikelets, with 5-17 florets on each spikelet, and the apical florets were not developed. The flower capital was glume flower. Each flower had a lemma and a palea, 3 lodicules, one pistil and 4-6 anthers (usually 6), each of them contained four pollen sacs. The anther wall belonged to the basic type with the typical glandular tapetum, and the cytokinesis was the successive forming the medianly zygomorphic tetrads. Mature pollen grains were 2cell type, spherical, with granular surface ornamentation, with a single germination hole, abnormal shrinkage and cavity aborted pollen grains in some anthers during pollen development. The pistil had unilocular ovary, anatropous, crassinucellate and double integument ovule and plumate stigma with three branches. The embryo sac was of the polygonum type, and the mature embryo sac was composed of an egg organ, a polar nucleus and antipodal cells. O. spongiosum was monochogamy and crosspollination. The fruit was caryopsis. The regeneration of bamboo forest was mainly sexual reproduction. (3) The whole O. spongiosum forest died after flowering, and the seed setting rate was low, and the seed setting rate was 8.1%. This research provides basic data for the study of bamboo flowering mechanism and regeneration of bamboo forest.