The current project is performed to gain an understanding of micro filtration by simulating gas flows through micro channels and micro orifices. The numerical simulation is based on the LBM. Both no-slip bounce-back and slip bounce-back boundary conditions are used to get the slip velocity at the wall under the various ranges of Knudsen number and Reynolds number. For the slip bounce-back boundary condition, the reflection factor and the accommodation coefficient are applied to obtain more accurate results. The results from the LBM simulation show that when the reflection factor is 0.85 the velocity and pressure profiles of the micro channel are in good agreement with the analytical results for Kn = 0.0194. In contrast, the accommodation coefficient scheme does not show good results for these micro flow implementations. From the velocity, density and pressure distributions of the micro orifice the compressibility effect is confirmed very well.