In recent years, the adverse effects of nanoplastics (NPs) and pyriproxyfen on aquatic environments have attracted widespread attention. However, research on their combined exposure to aquatic organisms could be more extensive. This work evaluated the acute and chronic toxic effects of polystyrene NPs (PS-NPs) and pyriproxyfen on Daphnia magna (D. magna) under their combined exposure conditions. The addition of PS-NPs within 24 h reduced the acute toxicity of pyriproxyfen to D. magna, resulting in an increase in the 24-h ECsub.50 values of pyriproxyfen on D. magna from 0.24 mg/L to 0.35, 0.51, and 1.26 mg/L, respectively when 1, 5, and 10 mg/L of PS-NPs were added. Compared with PS-NPs, pyriproxyfen significantly disturbed the growth and reproduction of D. magna in the chronic toxicity test at 21 days. The adverse effects caused by pyriproxyfen were alleviated when PS-NPs and pyriproxyfen were co-exposed. In addition, it was observed that the addition of pyriproxyfen resulted in less PS-NPs uptake by D. magna using a time-gated imaging technique. These findings provide new insight into the combined toxic effects of NPs and pyriproxyfen on the reproduction and growth of D. magna, and it is important to understand the effects of complex pollutants on aquatic systems. Moreover, it has provided an important scientific basis for environmental protection and sustainable development.