Heat pipe is a thermodynamic device of very high thermal conductance. In a heat pipe the working fluid experiences phase change both in the evaporator and condenser sections. The flat heat pipe (FHP) is a transmutation of the conventional heat pipes that finds applications to deal with high density electronic cooling problem due to their high thermal conductivity and reliability where large heat flux is to be transported through limited space. The paper presents a numerical analysis of two phase flow phenomenon in a flat heat pipe. The heat pipe modeling involves the principal physical processes of wick-liquid dynamics and movement of resulting vapour away from the evaporator through the heat pipe vapour space and into the condenser. The analysis involves the simultaneous solution of two dimensional continuity, momentum and energy equations in the liquid wick and the vapour core regions with respective boundary conditions. Two phase mixture model has been formulated to investigate the phase change phenomena. The incompressible flow equations for vapour-phase interaction with liquid particles are solved using appropriate under-relaxation parameters. Vapour flow in the vapour passage is assumed to be laminar and the heat dissipation at the condenser side is by forced convection. The axial vapour temperature and velocity distributions are obtained along the vapour core and liquid wick region at the steady state. The thermo-hydrodynamic characteristics of the heat pipe for a given heat input are predicted.