The invention discloses a trastuzumab bond-linking gold nanorod compound, a preparation method and application thereof in the diagnosis and treatment of HER2 positive breast cancer, which overcome the defects of poor regulation of photo-thermal conversion efficiency and incapability of location of targeting gold nanoparticles. The preparation method comprises the following steps: firstly, preparing a gold nanorod with a certain length-diameter ratio, wherein the longitudinal absorption peak is 650 to 850nm, and the nanorod is capable of meeting the optimal optical wavelength penetrating through tissue of a human body; then connecting cysteine with porphyrinfluorescent molecules, next, through the action of an Au-S bond, bond-linking the gold nanorod with a cysteine-porphyrin compound, finally through a glutaraldehyde chemical crosslinking method, bond-linking a gold nanorod-cysteine-porphyrin compound with a drug trastuzumab. The obtained trastuzumab bond-linking gold nanorod compound is capable of showing in-situ or micro metastatic focus, and performing a targeting photo-thermal therapy on a detected tumor focus, so that the difficult problem of drug resistance of tumor can be effectively solved.