Abstract: Hypersonic boundary layer transition plays an important role in aerodynamic design of hypersonic vehicles. Transition control is always one of the main purposes of the transition research. In the hypersonic flow, the roughness element is used to control the boundary layer transition. Firstly, this paper reviews the latest researches in hypersonic boundary layer transition control by various types of roughness elements in recent years. Then, from the perspective of the receptivity of the roughness elements to the hypersonic boundary layer and the crossflow stability, the role of the roughness element in the study of the hypersonic boundary layer transition mechanism is introduced based on the effect of the roughness element on hypersonic boundary layer transition. The application of the oil film interferometry technique in the study of hypersonic boundary layer transition induced by roughness elements in the hypersonic wind tunnel of Nanjing University of Aeronautics and Astronautics (NHW) is also briefly introduced. Finally, the existing problems in hypersonic boundary layer transition are discussed, and the future research trend is also prospected.