Abstract: The chalk river unidentified deposits (CRUD) on the surface of pressurized water reactors (PWR) fuel elements has many adverse effects on the stable and reliable operation of the system. Therefore, it is very important for the safe and high-quality development of PWR to study the key influencing factors of the CRUD on PWR fuel elements and to develop the mitigation technology of CRUD. This paper summarizes the important results of the experimental study on the surface CRUD of fuel elements in PWR, summarizes the harm of CRUD on the cladding surface to the operation of the system, reviews the analysis and characterization results of the CRUD, and introduces the test methods of the out-of-pile hydrodynamic loop established by different research institutions. The influence law of material properties, thermal-hydraulic characteristics, coolant chemical conditions and corrosion product characteristics on CRUD on the surface of fuel elements are analyzed. The CRUD mitigation technology and related applications are investigated, and suggestions for the follow-up experimental research direction are put forward.