In order to save the computing time of Monte Carlosimulation, traditional null collision method is improved in whichonly one cross section needs to be evaluated at each collisionspeed. By this method, the electron swarm parameters such aseffective ionization coefficient, $\bar{\alpha}$ , drift velocity and diffusioncoefficient of SF6 and CF4 gas mixtures are calculated overthe E/N range from 150 Td to 500 Td. A set of electron collisioncross-sections that gives transport parameters in agreement withmeasurements for the pure gases is used. The simulation results arethen compared with our experiment data, and show excellentagreements.