In this paper a numerical model is used for analysis of parameters which affects heat pipe operation. The steady state incompressible flows are solved in Cartesian coordinates in both vapour region and wick structure, using professional CFD (Computational Fluid Dynamics) software. The objectives of this work were to study of the parameters variation on the operation of heat pipes. The heat pipes are made from copper tube with the outer diameter 8.9 [mm ] and the length 200 [mm ]. The water is used as a base working fluid while the nanoparticles used in the present study are the iron oxide nanoparticles. Two cases, with volume concentration 0% and 2% for iron oxide nanoparticles are considered.