The invention provides a pharmaceutical composition for mild photothermal therapy of tumors as well as a preparation method and application of the pharmaceutical composition. The pharmaceutical composition is composed of a dual-targeting amphiphilic glucan derivative carrier, a material (PTA) with photo-thermal conversion performance and an autophagy inhibitor. The dual-targeting amphiphilic glucan derivative carrier can be self-assembled in water to form nano-micelles, and is physically loaded with PTA and an autophagy inhibitor for tumor photothermal therapy. The preparation is mainly characterized in that: 1) the preparation has active dual-targeting capability of tumor cells and tumor-related fibroblasts, and can efficiently enter the cells through the action of receptor ligands, so that the transfer efficiency of the preparation is improved; 2) under the irradiation of 808nm laser, PTA absorbs light energy and efficiently converts the light energy into heat, and the autophagy inhibitor inhibits the autophagy behavior of tumor cells and sensibilizes photo-thermal, so that an excellent mild photo-thermal treatment effect is realized, and the physical barrier of a tumor matrix can be weakened; tumor photothermal can further induce tumor cells to generate immunogenic cell death, generated tumor fragments can further activate an immune system, and the tumor photothermal treatment effect is greatly improved.