In order to monitor land subsidence in Tianjin area,a GPS network was established in 1995 as a complementary means of the precise leveling.

The relative altitude variations at these points were analyzed using ten years replicated observations in this paper,and they were compared with the results of precise leveling by the authors.

On the basis of the research on the contrast between GPS and precise leveling from 1995 to 2004, the actual accuracy of the two methods is tested.

The scheme of especial precision engineering survey should be comducted according to the accuracy requirement and the concrete conditions of the environment of the engineering,as well as the surveying instruments which can be used.

Aimed at different understanding and view point,based on precise level monitoring,GPS techniques and systematic analysis of in situ monitoring data of scores of years,the authors put forward a perspective of surface subsidence has certain self recoverable capability,summed up the range of surface recoverable subsidence threshold,narrated rational method and in situ monitoring essentials.

This is a report of the research about the Chinese mainland vertical motion with the help of the methods employed,results obtained in recent fifty years, using the materials of the national high precision leveling in three periods since the establishment of the People s Republic of China.