Abstract: On the consideration that the solid particle in wastewater invades into formation and plugs the pores so that reduces the inplace permeability, a mathematical model that is summarized as problem 1 and I roblem 2 has been developed. Problem 1 is a deterministic partial differential equation(PDE)reversed problem that can be solved with the difference format. In contrast, as a deterministic initial boundary problem, problem 2 has been solved with the method of characteristic, during which both the reservoir permeability and the damage radius could be found.The solving process of the two problems carries on in turns.

Key words: mathematical model, reversed question method of characteristic solve i