The aluminate coupling agent (ACA) modified expanded polystyrene (EPS) was used as aggregate to prepare plastic concrete by replacing sand and gravel in equal amount, and the effect of different aggregate content on the mechanical and thermal insulation properties of plastic concrete was studied. The results show that ACA modified EPS can significantly improve the mechanical and thermal insulation properties of plastic concrete. When the mass fraction of ACA modified EPS filler is 15%, the dry density of plastic concrete reaches 2 723 kg/m³, which is 51.21% higher than that of pure concrete. Compared to pure concrete, the compressive and flexural strength of plastic concrete increased by 19.09% and 18.38%, respectively. The average friction coefficient of plastic concrete is maintained at 0.66. When the mass fraction of ACA modified EPS filler is 25%, the thermal conductivity of plastic concrete reaches the lowest, which is 0.12 W/(m·K). After comprehensive consideration, it is recommended that the replacement amount of ACA modified EPS aggregate be 15%. At this addition amount, plastic concrete exhibits excellent mechanical, wear resistance, and thermal insulation properties.