brain drain
noun [ S ] uk/ˈbreɪn ˌdreɪn/ us/ˈbreɪn ˌdreɪn/
（国家的）人才流失，人才外流
the situation in which large numbers of educated and very skilled people leave their own country to live and work in another one where pay and conditions are better
Britain has suffered a huge brain drain in recent years. 英国近年来人才外流现象十分严重。