Ovoviviparity is a reproductive strategy evolved by fish to adapt to specific environment. Gambusia affinis is a typical ovoviviparity fish. Clarifying whether its ovoviviparity characteristics have adaptive evolution in the process of invasion into the Yunnan-Guizhou Plateau will help us to understand the mechanism of its rapid population spread. Therefore, we conducted the research on the characteristics of embryonic development, changes in dry and wet weight, and the relationship with maternal nutrition in G. affinis Dianchi Lake population using conventional anatomical observation and weighing methods. The results showed that the embryonic development process of Dianchi Lake population depended on the supply of yolk nutrition. Before production, the yolk was basically consumed, and the body developed well, basically maintaining the inherent ovoviviparity characteristics of the species. The wet weight of embryos increased significantly during embryonic development, but at the same time, the dry weight loss was also very obvious (30.4%), and the nutrition index (matrotrophy index, MI) was 0.70, which suggested that the mother had no specific nutrition supply for embryos after fertilization, supporting the view that the G. affinis was a strictly lecithin trophic (ovoviviparity) fish. The embryo (fry) shows a trend of miniaturization, and key ecological adaptive traits such as wet weight, dry weight, and initial body length of the embryo are significantly lower than other lowland populations that have been studied, demonstrating an adaptive response to plateau environments. Whether this response contributes to its diffusion in higher altitude plateau environments deserves further in-depth research.