Abstract: Gas flows driven by pressure in a microchannel are computed with the direct simulation Monte Carlo (DSMC) method. The rarefied effect is observed and slip velocity exists at solid boundaries. Temperature is almost constant in the whole flow field. The Mach number of the flow is very low. Density and pressure vary significantly along the channel while they are nearly invariant transversely. Nonlinearity of pressure distribution along the channel due to compressibility is found and reduces as the Knudsen number increases.