Aiming at the balancing/rebalancing problem of mixed-model assembly line(MMAL) caused by customer demand changes, product design development and assembly technology and equipment upgrades, the contents and research progress of MMAL are summarized. Firstly, the research progress and the planning methods are described in the balancing and rebalancing of MMAL. Then, the classification and general solution for MMAL balancing problems are summarized. Finally, this paper puts forwards the future research consideration on the balancing of MMAL.