The back-analysis of mechanics parameters of surrounding rock of cave needs forward calculating again and again,resulting in low efficiency,and the development work of coupling the optimizing code and forward numerical simulation code is very much.In order to solve these problems,a new method for the back-analysis of mechanics parameters of surrounding rock of cave was proposed by combining particle swarm optimization algorithm and FLAC numerical simulation analysis.The theory and calculating flow of the method are discussed,and the computing program is developed using FISH,embedded language of FLAC3D.A computation example proves that this method has rapid convergence and high precision.