Abstract：Although the anchor cable is widely used in the geotechnical projects，the prestress variation rules of the anchor cables are still not clear，especially the prestress loss when being locked and lasting of prestress variation of cable in cracked rock are interesting issues. Based on the in-situ monitoring results and analysis of a slope reinforcing case，the prestress loss under being locked，and short-term as well as long-term prestress variation rules are studied. The influence of multi-factor on the anchor cable prestress state is discussed. These factors include the relaxation of the anchor cable，the compression of surrounding rock，the environment change of surrounding rock，and so on. The short-term and the long-term prestress losses are both nonlinear，which can be divided into three stages：remedial loss，long-term loss and periodic variation. The former factors include the friction between anchor cables and surrounding rock，deformation of anchorage system，uneven stress distribution，excavation of the next step slope，the impact action，the effect of group cables，most of which found in the construction term can be retrieved by tensioning again. The long-term prestress loss can be caused by the compression of surrounding rock and relaxation of the anchor cable，which shows the notable interaction effect. Influential factors of the periodic variation include rainfall and temperature change and the variation amplitude is not small and it can return to the former condition. As for the long-term prestress loss of the anchor cable that is trigged by the creep of the materials，a new mechanical model is established and the forecast equation is derived，which presents the interaction of the compression and relaxation. By means of the mechanical parameters and monitoring data of the practical engineering，the stability of the prestress anchorage engineering can be analyzed.
