In this study, slip-flow heat transfer in a laminar, steady state, two-dimensional incompressible flow betwee parallel plates micro channel is investigated. Both hydrodynamically and thermally fully developed flow case is examined. A new method for modeling of micro-flows is presented. Navier-stokes equations are developed by using perturbation expansions of velocity, pressure and temperature fields. Different orders of equations in dependence of Knudsen number are obtained. In this study three-term expansions are used, so three set of equations are obtained. Each set of these equations are solved. The computations are performed for micro channels with CHF (Constant Heat Flux) and CWT(Constant Wall Temperature) boundary conditions to obtain heat transfer characteristics of gaseous flow in slip regime. Slip boundary conditions used to solving governing equations. The effects of creep flow and viscous dissipation are neglected in this study. The numerical methodology is based on Semi-Implicit Method for Pressure-linked Equations (SIMPLE) method. The effect of Knudsen number on Nusselt number and friction factor is numerically determined. It was found that Nusselt number and friction coefficient were substantially reduced for slip flow regimes compared with the continuum flows. The obtained solutions are compared with both available numerical and analytical results and found that present results has good agreement with other works. Also in present study the effects of Axial heat condition, Thermal creep flow and accommodation coefficients on heat transfer rate are investigated separately. Obtained results are compared with other researcher results that are available and found that there is a good agreement between them. It is shown that when Peclet number decreases, the role of axial heat conduction in heat transfer become more important. For thermal creep flow, it is found that if temperature gradient has a same direction with main flow, heat transfer rate increases. The study on role of accommodation coefficients variations shows that increasing in thermal accommodation coefficient lead to increasing in heat transfer rate and increasing in momentum accommodation coefficient decreases the Nusselt number.In all this results, it is found that when Knudsen number is increasing, deviation from analytical results is increasing. So in this method, for high Knudsen number we should use more terms in perturbation expansions. Key Words: heat transfer, slip-flow, micro-channel, parallel-plates, Nusselt number, perturbation expansion.