In order to develop an excellent Au nanostars therapeutic agent for photothermal therapy and optical coherence tomography, we research the preparation of gold nanostars, photothermal properties, photothermal therapy and applications in optical coherence tomography. By adopting the tip structure to enhance the local surface plasmon resonance properties of gold nanomaterials, the multi-branched Au nanostars is prepared by seed mediated method. The multi-tip structure enables the Au nanostars to have obvious photothermal effect, then its effect as a therapeutic agent for photothermal therapy and contrast agent for optical coherence tomography is explored. The experimental results showed that compared with Au nanoparticles, the multi-branched Au nanostars had a higher photothermal conversion efficiency of 42%, and has good biocompatibility. At the concentration of 100 μg/mL, the survival rate of human breast cancer cells is 82%. Human breast cancer cells are effectively killed by laser irradiation at the concentration of 100 μg/mL, and the survival rate is significantly reduced to 37%. At the same time, Au nanostars also has better optical coherence tomography imaging effect, significantly improving the signal intensity and imaging depth. Au nanostars is a promising multifunctional therapeutic agent with both efficient photothermal therapy and excellent optical coherence tomography imaging capability.