Carbon capture, utilization and storage (CCUS) is recognized as a critical strategy for achieving China's "dual carbon" goals. As a vital component of CCUS, CO₂-enhanced oil recovery (CO₂-EOR) improves hydrocarbon production through CO₂ injection into reservoirs while enabling partial CO₂ sequestration, thereby achieving synergistic environmental and economic benefits. The phase behavior characteristics of the crude oil-CO₂ system during CO₂ flooding in the low-permeability reservoirs of Block X, Ordos Basin was focused. High-pressure physical property analysis and phase behavior experiments were conducted to obtain key parameters, including crude oil volume factor, viscosity, density, and saturation pressure. Experimental and numerical simulation approaches were integrated to further analyze the effects of CO₂ injection on phase behavior. The results indicate that the density, volume factor, and saturation pressure of crude oil in Block X are significantly influenced by pressure variations. CO₂ injection is observed to enhance reservoir pressure, reduce crude oil viscosity, and modify the phase behavior and miscibility degree of the crude oil-CO₂ system. Pore size is identified as a critical factor affecting phase behavior: smaller pores with stronger capillary forces exhibit more pronounced impacts on crude oil properties. In median-sized pores, increased CO₂ injection reduces viscosity, decreases density, and enhances the volume factor. It is concluded that CO₂ flooding optimizes crude oil phase behavior and improves the development efficiency of low-permeability reservoirs. The research results provide theoretical insights into the phase behavior evolution during CO₂-EOR processes, offering guidance for enhancing oil recovery in similar reservoirs.