Abstract：The Lianziya dangerous rock-body control engineering in Three Gorges Reservoir of Yangtze River lasted 51 months from beginning in May，1995 to finishing in Aug. of 1999. Engineering effect monitoring conducted for five years for Lianziya up to Dec. of 2004 and tested by water table 139 m of Three Gorges Reservoir after Jun. in 2003. Three factors，i.e. monitoring data about deformation in the surface of Lianziya，pressure in coal mined-out area and calculation results of stability，are united as a scientific criterion to access engineering control effects. It can be seen from deformation monitoring data that Lianziya becomes stable gradually because the horizontal displacement velocity is decreased from about 2.0 mm/a to less than 1.0 mm/a and vertical displacement velocity from about 1.5 mm/a to less than 0.75 mm/a before and after engineering control. Lianziya stability is extremely susceptible to response to constructing activity in coal mined-out area，where the horizontal velocity of surface monitoring points was about 8.0–18.8 mm/a and vertical velocity about 8.0–21.0 mm/a in engineering working period from May of 1995 to Aug. of 1999. It is proved that stress concentration and relaxation belt is existent resulting from the effect of cantilever plate with inclined pressure in coal mined-out area. In the lowest layer most of pressure data on the concrete key system for bearing pressure and anti-sliding are between 2.0 and 10.0 MPa，but the maximum and minimum values are 18.08 and －0.8 MPa，respectively. All the data are almost constant since Jan. of 2002. Displacement velocity change is not obvious and pressure values change is less than 0.01 MPa in Lianziya when water table rises to 139 m in Three Gorges Reservoir of Yangtze River after Jun. of 2003. Lianziya control engineering has achieved designing goal based on the stability coefficient greater than 1.15 in special loading condition and 1.30 in general. The large size(1 m×1 m) rockmass mechanics test was made in field to obtain the strength parameters for stability calculation of the engineering.
