Nanotechnology is a hot spot of cutting-edge scientific and technological research in today's society. It is widely used in nano-drug carriers, functional nano-materials, nano-biosensors and micro-devices, and has promising applications. The purpose of this paper is to study the application of nanotechnology in biomedicine. A CT imaging-guided tumor photothermal therapy nanomedicine, Bi2S3 nanoflowers, is proposed. Based on the high X-ray attenuation and near-infrared absorption properties of Bi, and the high specific surface area of Bi2S3 nanoflowers, Bi2S3 nanoflowers have excellent CT imaging and photothermal treatment effects. On this basis, we first evaluated the characterization of Bi2S3 nanoflowers in the experiment, and confirmed that Bi2S3 nanoflowers are a kind of biosafety nanomedicine by evaluating the efficacy of bismuth sulfide nanoflowers at the cellular level. At the same time, it was confirmed by flow cytometry results and 4T1 live-dead staining data that Bi2S3 nanoflowers as a photothermal therapy drug induced significant tumor cell death.