Abstract: To consider the effect of environmental pressure, We have modified the MacArthur-Wilson equilibrium model to be used in the PFU method, and derived a more suitable model. four function parameters that are used in the biological evaluation of environment are brought forward from the field ecological effect tests and the laboratory toxicity tests. A computer program was elaborated to calaulate, the parameters, using Monte Carlo sequential stochastic simulation method and Marquardt's method. The lack of fit test(LOF Test)was used to verify the model against empirical data.