Upconversion luminescent nanomaterials have the significant advantages of long fluorescence lifetime, low potential biotoxicity, large penetration depth, small damage to biological tissues and few background light. In recent years, photodynamic therapy, bioimaging and biological detection have been widely used, but in the process of application, there are some problems such as low efficiency of energy transfer between UCNPs and target, overheating of normal tissues. In biological imaging, the fluorescence intensity is weak, the photosensitizer and activator have energy reflow, and the imaging mode is single. Researchers have developed a lot of solutions to these problems, such as shortening the distance between UCNPs and targets, changing the intensity of laser irradiation and the structure of UCPs, integrating UCNPs as a new multifunctional platform for imaging and treatment, etc., so that some of the problems are well solved. This review focuses on the solutions to the problems that arised from the use of UCNPs in PDT and bioimaging. The future development of UCNPs in biomedicine is also discussed.