Prediction of Remaining Useful Life (RUL) of lithium-ion battery is important contents of battery management. It is of great significance to prolong battery life and ensure the reliability of battery system. Researchers all over the world have done a lot of research on battery RUL prediction and proposed a variety of methods. This paper first introduces the definition of RUL, then classifies the main methods into three kinds. This paper also introduces and compares these methods. Finally, the challenges of lithium-ion battery RUL prediction methods are summarized, and the future research direction is proposed.