On the basis of the Gauss's law,two sets of implicit potential equations describing the changes of surface potential and back one with gate voltage are established for asymmetrical dual gate a-Si: TFT thin film transistors.Then,a unified channel potential model with two independent gates is constructed by solving 1-D Poisson equations.This model can be simplified to a symmetric dual gate model under given conditions.In addition,most of relevant parameters can be physically extracted from real experimental data and only few fitting parameters are involved.On this basis,a novel scheme for the approximation of surface potentials is proposed by means of mathematical transformation and by using the Lambert W function.Numerical results show that the proposed scheme is of better convergence and the approximation of those potentials can be directly used to set the initial values of simulation tools,which effectively improves the computation efficiency of self-consistent solutions to the constructed model.