Poly(lactic acid)/thermoplastic polyurethane/titanium dioxide (PLA/TPU/TiO₂) composite films were prepared using a solution blending-melt hot pressing technique. The effects of the mass fraction of thermoplastic polyurethane (TPU) and the addition of titanium dioxide (TiO₂) on the mechanical properties, thermal stability, hydrophilicity, and UV resistance of the composite films were systematically investigated. The results revealed the synergistic mechanism between the elastic phase of TPU and the rigid phase of TiO₂. When the mass fraction of TPU was 20%, the tensile strength and elongation at break of the PLA/TPU composite film reached a balance, with values of 45.89 MPa and 17.89%, respectively. On this basis, the addition of 2% TiO₂ further increased the tensile strength of the PLA/TPU/TiO₂ composite film by 11.5%, reaching 51.17 MPa, while the elongation at break increased by 83.29%, reaching 32.79%. The addition of TiO₂ significantly optimized the crystallinity and hydrophilicity of PLA. When the mass fraction of TiO₂ was 3%, the ultraviolet protection factor (UPF) of the PLA/TPU/TiO₂ composite film reached 87.35, and its thermal stability was significantly enhanced. The study demonstrated that the synergistic effect of TPU and TiO₂ not only achieved simultaneous toughening and strengthening of PLA but also improved its thermal stability and UV resistance. The prepared PLA/TPU/TiO₂ composite films possess both environmental friendliness and functional application potential, and the research provides support for the development of high-performance biodegradable films.