In this research, upconversion nanoparticles (UCNPs) are used as a light conversion carrier, and their deep light source penetrability is closely combined with ultrathin two-dimensional (2D) Ti3C2Tx to explore the application efficiency of the complex in phototherapy. Due to the advantages of 2D Ti3C2Tx with its high absorbance to ultraviolet/visible light, rich atomic defects to load the drugs, and adjustable thinner structure, this 2D material is beneficially applied as the energy donor. UCNPs@Ti3C2Tx with a photothermal conversion efficiency of 20.7% is proven with the ability to generate reactive oxygen species under a 980 nm laser at the cellular level. Importantly, the main photothermal therapy method can be changed to a photodynamic therapy method due to the degradation of Ti3C2Tx to TiO2 under the oxygen-bearing environment. The in vivo experiment was continued to verify that UCNPs@Ti3C2Tx can kill tumor cells and inhibit tumor growth within a certain period. In addition, in vivo treatment with a combination of immunotherapy and phototherapy of UCNPs@ Ti3C2Tx is carried out to achieve stronger tumor inhibition over the prolonged time points.