对国际原子时（TAI），地球力学时（TDT）和质心力学时（TDB）的定义和概念作了回顾和阐述。对其中一些有争议的问题进行了介绍和讨论。
This paper reviews the definition and conception of TAI , TDT and TDB , introduces and discusses some problems which are disputed recently among astronomers and physicists .
质心力学时