The invention relates to a preparation method of a gadolinium oxysulfide (Gd2O2S) gold nanorod core-shell structure. The preparation method comprises the following steps: preparing seed crystals, preparing a growth solution, preparing gold nanorods and preparing the Gd2O2S gold nanorod core-shell structure (GNRs@Gd2O2S). The modified gold nanorod @ gadolinium oxysulfide (Gd2O2S) and the preparation method thereof have the characteristics as follows: the preparation method is simple and repeatable, the biocompatibility is good, and good light-heat conversion efficiency is achieved; besides, both magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) can be carried out, the diagnosis and treatment of tumor are combined, and good biological-medical and cancer therapic application prospects are achieved.