We systematically studied the reproductive characteristics and gonadal development of the threatened freshwater mussel Solenaia oleivora from the Huaihe River. This species is not only threatened, but it also holds important economic value in China. The results indicate that this mussel has a short-term incubation and spawns from March to early June, peaking from March to May. The youngest gravid female investigated was 2 years old. During the reproductive period, the female oocytes mature rapidly and release several times in one reproductive cycle. The inner and outer gills of the female could be utilized as the marsupia for fertilized egg incubation, which belongs to Tetragenae in Exobrandae. The total number of glochidia in the gravid female mussel is estimated to be 1.349 to 4.021 million for a single egg release event. Based on female gravidity and the ovary tissue sections, we confirmed that S. oleivora could release eggs several times in one reproductive cycle. There were no significant differences in the growth of males and females. The development of the ovary and spermary were synchronous and can be divided into the proliferating, growing, maturing, releasing, and recovering stages. Histological sectioning and scanning electron microscopy (SEM) showed that the oocytes are linked to the follicular wall through a stalk approximately 5 μm in diameter. There was no cell membrane on the surface of early oocytes < 20 μm in diameter, but a yolk-membrane was observed on the surface of late oocytes when the diameter was > 40 μm. SEM showed that the sperm had a long flagella (~40 μm long) and a bullet head and neck with a maximum width of~2 μm. There was a round micropyle (1 μm in diameter) on the surface of the fertilized egg, suggesting that sperm cannot completely enter the oocyte for fertilization. The results of this study provide a foundation for the artificial breeding of this mussel species in China and serve as an important reference for the breeding and conservation of other threatened or endangered freshwater mussels.