Abstract: In this work, we established a heat transfer model for heating phase in the rotational molding process from mold heating to powder melting. In this model, the temperature gradients of the mold, internal air and powder were ignored, and their average temperatures only varied with time. The space inside the mold was divided into the internal air region and powder region. Heat was transferred from the mold to both internal air and powders by convection, and meanwhile, heat was also transferred from internal air to powders by convection when they were mixing. The heat equilibrium equations for the mold, internal air and powders were presented on the basis of the principle of energy conservation. Furthermore, the analytical solutions for their average temperatures were obtained by simplifying and solving the differential equations. The internal air temperatures calculated from the analytical solutions were in good agreement with the experimental results, thus proving the validity of the heat transfer model and its analytical solutions..