Two dimensional numerical simulation is presented for flow and heat transfer in rectangular microchannel with uniform wall temperature in slip regime. Numerical solutions are performed for the velocity and temperature under the first order slip boundary conditions. The influences of different Kn numbers on the slip velocity and jump temperature are investigated. The results show that the gas rarefaction makes the pressure distribution more linear. Both the slip velocity and jump temperature at the inlet and outlet of the microchannel increase with the increase of Kn numbers. The gas average velocity and mean temperature increase greatly at the channel entrance, and both the temperature and velocity at the channel exit decrease with the increase of Kn numbers.