The investigation on the spot indicates that the main environ-geological cause for the destruction of sites and degradation of cultural relics is the seepage of groundwater. The water-control is thus a chief geotechnical engineering for the preservation. The following are the principles of the sites’ preservation in situ: 1. The moisture content of the culture relics and the rock around the sites must be less than 40%; 2. The groundwater level must be under the level corresponding to the soleplate’s altitude of the sites subtracting the capillary height of the groundwater; 3. The geological engineering for the long-term preservation of the sites must keep steadily and normally running; 4. The geological engineering must harmonize with the sight of the cultural relic. According to the principles of the sites’ preservation, the following basic technical ideas of the control-water project are put forward: 1. Find out the hydrogeological and engineering geological conditions of the sites; 2. Build up the hydrogeological model of the sites’ region; 3. Analyze the problems of engineering – geology and environ – geology; 4. Demonstrate the scheme of the control-water project for the sites’ preservation; 5. Optimize the design of the control-water project; 6. Carry out the control-water project. Moreover, the key to find out the hydrogeological condition and the changing regularity of the seepage field of groundwater in the sites is pointed out. The numerical simulation technique can simulate the changing regularity of the seepage field. The Canoe site in Xiaoshan region of Hangzhou is taken as an example to explain the technology. On the base of the hydrogeological conditions in the sites, the original water distribution is simulated. According to the engineering geological conditions and the result of the fore-going simulation, a scheme of draining the groundwater around the sites is brought forward. The simulation and forecast of the changing regularity of the groundwater-seepage field in the sites after the water-draining show that the scheme is plausible and can be utilized to aid the design and construction of the water-control project.