Abstract: Naphthalene (Nap), as one of the main types of polycyclic aromatic hydrocarbons pollutants, widely exists in China’s aquatic environment. Micro-plastics (MPs) can easily become an excellent carrier of persistent organic pollutants and form compound toxic effects on aquatic organisms. However, there are few studies on the acute toxic effects of these two pollutants combined. In order to understand the joint toxic effects of polycyclic aromatic hydrocarbons (PAHs) and microplastics, the algae density, chlorophyll a (Chl.a), Soluble protein (TP), malondialdehyde content (MDA), catalase activity (CAT) and superoxide dismutase activity (T-SOD) were measured for studying the acute toxic effects of Nap combined with MPS on Chlorella vulgaris, which is an indicator of ecological environment. The results showed that C. vulgaris could be inhibited by both nap and MPs. The highest inhibition rates were 68.26% and 78.36% respectively under single stress, and 52.05% under combined stress. The inhibitory effect on Chl.a was consistent with the algae density. Under single and combined stress, TP content decreased and MDA content increased significantly. The activities of CAT and T-SOD decreased significantly under Nap stress. The activities of CAT and T-SOD increased first and then decreased under MPs and combined stress. The final activities of CAT and T-SOD of the combined stress experimental group were significantly higher than the control group. The EC₅₀-96h of Nap and MPs on C. vulgaris were 81.35 and 383.3 mg/L, respectively. The toxicity of Nap was stronger than MPs. The EC₅₀-96h of Nap combined with MPs (toxic unit ratio 1﹕1) on C. vulgaris was 1.320 TU. The results showed that joint toxic effect of the two pollutants hasn’t been more significant than single pollutant, and the joint toxic effect on C. vulgaris was antagonistic. MPs played an adsorption polymerization role on Nap, which greatly reduced the probability of contact between both pollutants and C. vulgaris. The existence of MPs showed a certain protective effect in the short term.