The successful launch of the GRACE twin satellites in March, 2002 for gravity and climate study, which is a US and Germany co-sponsered project, will deliver time-varying gravity models with unprecedented precision. The two identical satellites are about 220 km apart on a nearly polar orbit with an altitude of 300－500 km. On aboard GPS data and accelorometer mearuments are used to precisely determine the orbits, and raange change rate measurements between the twin satellites are used to recover gravity to much higher precision than before at spatial scales of a few hundred km and larger. The mass redistribution data derived from the GRACE time-varying gravity models will have profound impacts on various geophysical research topics. Despite of its designed 5-year lifetime, simulation studies have shown that the GRACE gravity will provide important information on secular change of ice sheets, and global mean sea level change. At seasonal time scales, GRACE gravity is capable to detect land water change less than 1 cm or change in oceanic bottom pressure less than 1 mbar. Besides social and economical importance, knowledge in mass redistribution helps us understand both water mass and energy transfer. The purpose of this paper is to provide necessary background for understanding various prosesses of mass redistribution, and to propose application studies focusing on China and neighboring oceans.