With the development of the world, the energy crisis has become increasingly prominent, which has greatly affected the sustainable development of the global economy. To ease the energy crisis and move towards sustainable development, the recovery of low-grade waste heat has gained increasing attention. Through a literature tracking strategy, this report provides the current state of research on internal leakage of the scroll expander, a key component of the organic Rankine cycle system. The structure, working principle, heat transfer and expansion efficiency of the scroll expander are introduced. The types of internal leakage, calculation model of leakage, influencing factors, influencing factors and solutions are analysed in detail. The main influencing factors of internal leakage are axial clearance, radial clearance, speed, air pressure, lubricating oil and so on.