Abstract: To infuse water into oil reserrvoir by high-pressure pump,then the oil residua flow out of oil well,this is a problem of two-phase immiscible flow displacement,where are an important means of the modern oil extracting process. The mathematical model of the problem is the initial boundary problem of systems of partial differential equation.We have set up some computational scheme by the numerical method of differential discrete operator,also we have studied approximute and convergence theorem of continuous-time approximation and discrete-time approximations. At last, we have computed the two-dimensional problem by using the numerical method,the computation result is rational and shows the stability of the methods.