The deformation monitoring items of the dam for Shanxi Hydropower Station include the elevation control network close to the dam area, plane control network of triangulation and trilateral, dam collimation line and settlement monitoring.

Through the actual building of the three-dimensional control network,this article has carried on the analysis and the discussion to the precision of GPS horizontal control network and the elevation control network built by the digital level,and proposed several beneficial opinions to make the two more effective combination.

Considering the rapid development of space and information technology,Chinese national height control network,as one of the backbones of geographical spatial fundamental infrastructures,is necessary to be updated and modernized.

When the height control network is observed periodically,whether the point difference is caused by the observation error or is really subsident must be distinguished.

The article introduces how to compile programme and to estimate the precision of vertical-control net with ad- justment conditions and indirect adjustment,in order to realize the optimized design of vertical-contral net simulation,and finally to give an example.

According to the precision demands of vertical control for large bridgeconstuction, this paper calculated the necessary precision of vertical control network andput forward a layout and observation program for a certain large bridge construction.

The constructing method of GPS height control network of city was discussed.