Abstract: In this paper, a new dynamic distillation model(simulation algorithm) has been derived. Because of the use of linear algebraic equations derived from enthalpy balances to solve for the ascending vapor quantity, and the use of differential equations for all other variables, the divergent problem caused by the iteration of nonlinear equations for the attainment of bubble point or dew point temperatures can be avoided. The large dynamic model of a dehex-anizer of seventy plates and six components(differential equation with an order of more than six hundred) has been calculated successfully by an integration method for solving stiff ordinary differential equations-numerical small parameter method. The conspicuous advantage of the method is no need of Jacobian matrix calculation and its inversion.