Photonic crystal hydrogel is an advanced material that combines the properties of photonic crystal and hydrogel with unique responsiveness and optical properties. By combining photonic crystals with hydrogels, the new material not only inherits the optical properties of photonic crystals, but also possesses the responsiveness and good biocompatibility of hydrogels. This makes the photonic crystal hydrogel show a broad application prospect in the field of sensors, clinical detection and biomedicine. In recent years, the use of photonic crystal hydrogels for sensors has been studied and applied. By designing different photonic crystal hydrogel materials, the temperature, humidity, and ion concentration in the environment can be targeted for highly sensitive detection. The results of the detection will be fed back in real time as visualized optical signals, i.e., changes in structural color. The material has been little studied in the clinical detection and biomedical fields and deserves further exploration. In this review, we first introduce the basic information of photonic crystal hydrogels, such as the structure and synthesis of the material. Then, we further describe the current research progress and preliminary results of this material in the fields of biosensing, drug release and clinical detection.