Photothermal therapy (PTT) utilizes photothermal materials to convert light energy into heat under external light irradiation, effectively killing cancer cells. Therefore, the efficacy of PTT is largely determined by the photothermal conversion efficiency of the material. In this study, we developed a novel ladder-type conjugated polymer, PPAPA, a phenazine ring fusion reaction. PPAPA exhibits a high photothermal conversion efficiency of 75.2 % under 1064 nm laser irradiation, comparable to the benchmark organic photothermal agent SWCNT. Notably, the synthesis of PPAPA avoids the use of noble metal catalysts, eliminating potential biotoxicity caused by residual catalysts and ensuring optimal photothermal stability and efficiency. Furthermore, PPAPA demonstrates efficient photothermal conversion under near-infrared II (NIR-II) 1064 nm laser irradiation, enabling deeper tissue penetration and reduced tissue absorption. This work comprehensively investigates the photothermal properties of PPAPA and evaluates its efficacy in tumor PTT, demonstrating its potential as a novel and effective therapeutic strategy for cancer treatment, offering new hope for patients.