There are many fractures in natural rock mass. The stability of rock engineering is severally affected by the seepage of water through these fractures. So

determination of the permeability coefficient of those fractures is very important. The back analysis is a suitable method to determine those parameters. But it is a complicated optimum problem of nonlinear function of back analysis of seepage parameters for rock mass. To solve this problem

there exist a lot of shortcomings to use traditional optimum methods

including genetic algorithm. So

a more suitable bionics algorithm

immunized evolutionary programming proposed by the author is used to solve this problem. At last

this new back analysis method is tested by a typical example. The results show that

the permeability coefficients by proposed algorithm are close to the real ones that can be gotten only through the known water head results.