A numerical simulation tool for Schottky-Barrier Carbon Nanotube Field-Effect Transistors (SB-CNFETs), based on self-consistent solution of Poisson and continuity equations was developed. Method of moments is used for solving Poisson equation. Continuity equations are solved using current boundary conditions. Boundary currents are those currents tunneling through Schottky barriers at the contacts, which are calculated numerically using transfer matrix method. Regarding long devices, we have exploited the fact that, except near the contacts, the potential on most of the channel length is slowly varying to reduce the computational burden. During the solution of Poisson equation, mapping this part of the device into much smaller length has no perceptible effect on the accuracy of solution; however, it saves much of the simulation time and memory and allows the calculation of transport characteristics inaccessible to classical techniques.