By artificial culture,with semithin section and ultrathin section,we continuously observed the whole procedure of sexual reproduction of Isoetes sinensis Palmer.The results showed:(1)both female and male gametophytes are intramural development,there are rhizoids and archegoniums on femal gametophyte;but no rhizoids for male gametophyte,and every male gametophyte have 4 spermatids,all of them have 8-12 flagellums.(2)There are only two neck canal cells and one egg in the archegonium,and the ventral wall cells were transformed from the gametophyte vegetative cells.(3)Between the first division of the zygote and the achegonium’s long axis,there is an angle about 20°,and the embryo with 2-4 cells is easy to division and be aging,organization differentiation obvious on the embryo after 10 cells.(4)When is the globular embryo’s time,the first leaf has not differentiation and ligule primitive cell appeared in the embryo.The first leaf ligule will not development until the first leaf’s upside change to green and get photosynthetic capacity.The results supported the view of the priority development of root and leaf,and we think the main reasons of the I.sinensis endangered are about the male gametophyte’s lower germination rate and the female gametophyte exist more abortive structures.