Abstract: The computational domain was meshed by Delaunay triangulation method.A Monte Carlo direct simulation program was developed for unstructured grids and its validity was checked.On that case,the two-dimensional flow and heat transfer of rarefied gas in parallel plate micro-channels with triangular roughness elements were simulated.The pressure of the micro-channels' inlet and outlet and the temperature of the plates above and below were constant.The influences of the height,width and distribution density of roughness elements were computed and analyzed.The results show that roughness elements in the micro-channels can create obvious disturbance for the flow and heat transfer.The greater the roughness elements,the more visible the oscillation of velocity,even vortexes occur,which increases the pressure loss;but roughness elements can enhance the heat transfer.