Belonging to the field of medical technology, the invention in particular relates to a rosuvastatin calcium impurity, a preparation method and application thereof. The impurity and related optical isomers thereof can be separated after photodegradation of rosuvastatin calcium oxidation impurity III and optical isomers thereof or rosuvastatin calcium IV and related optical isomers thereof. The impurity is discovered for the first time, and the standard product of the impurity can be used for qualitative analysis and quantitative detection of impurities in rosuvastatin calcium drugs, solves thetechnical problem of lack of a standard substance of the impurity for analysis and comparison at present, at the same time solves the problem that illumination degraded unknown impurities cannot be effectively attributed in the drug research process, and provides the thinking for in-depth study of the degradation pathway and degradation mechanism of rosuvastatin calcium drug, thereby laying the foundation for research and development of safer, more effective and quality controllable rosuvastatin drugs.