The Casimir interaction between a suspended metallic plate and a VO₂/PS phase-change composite nanofilm in a liquid environment is investigated. By exploiting the metal–insulator phase transition of VO₂, the electromagnetic response of the VO₂/PS composite nanofilm is systematically described using the Maxwell–Garnett, Cuming, and Bruggeman effective medium models. Based on these models and Lifshitz theory, the Casimir pressure is calculated and analyzed as a function of separation distance, filling fraction, film thickness, and temperature. The results show that the Casimir pressure strongly depends on both the VO₂ filling fraction and its phase state. Within a specific range of filling fractions, the temperature-driven phase transition of VO₂ enables a reversible transition of the Casimir interaction between long-range attraction and being a stable equilibrium state. As a result, the system allows for the creation, elimination, and continuous tuning of Casimir equilibria. This work provides a multi-parameter control of Casimir equilibria using phase-change composite materials and offers theoretical guides for the precise manipulation of Casimir interactions at a micro/nanoscale.