A method of tracking specific cells in vivo is disclosed. The method of the disclosure includes: providing fluorescent nanoparticles suitable for targeting of specific cells; administering the fluorescent nanoparticles to a subject; providing an X-ray source to irradiate the subject; and determining the distribution and growth of the specific cells by the fluorescent images from the fluorescent nanoparticles and X-ray images of the subject irradiated by the X-ray source.