Abstract：The flexible protection system has been widely used in slope protection against geological hazards. However，the design of this system is mainly preformed based on the experience of engineers. Few methods can be used to evaluate the slope stability. A new method for evaluating the stability of the slope protected by flexible active protection system is put forward. First，the strengthened force of unit steel wire net can be obtained by analyzing the steel wire material. Secondly，the boundary of the maximal potential fail rock block can be determined by field investigation，and the safety factor of the rock block can be calculated through the formulae deduced from the classical wedge theory. In practical calculation，the designer can define the design safety factor beforehand，and the volume of the maximal rock block protected by the flexible system can be obtained based on field investigation. The comparison between the maximal volume and the field rock blocks is made. If the maximal volume is larger than all the field rock blocks，the stability of the slope is acceptable. Otherwise，the slope must be reinforced.
