We have successfully created a Direct Simulation Monte Carlo (DSMC) model on a commercial FEM software COMSOL Multiphysics (COMSOL). As far as we know, this is the first DSMC model developed on COMSOL. Since two particles as a colliding pair cannot be sampled simultaneously from the same population in the Particle-tracing module of COMSOL, a new inter-molecular collision scheme named “quasi-Nanbu