An automotive headlamp which is necessary for nighttime driving was used as a only safety part in the past, but, a latest headlamp are increasingly required not only to be a function but also to enhance a design of an automobile. These new demands make a headlamp complicated in a structure, therefore, if heat transfer and flow inside a headlamp can be predicted in a design stage using the Computational Fluid Dynamics (CFD), a deformation of plastic parts by heat can be avoided, and a misting problem on a lens due to humidity control performance of plastic parts can be also predicted. As a result, this will enable to shorten a development period. In this paper, a newly-developed method called surface heat transfer (SHT), a unique technique for making an accurate estimation of temperature and velocity in an automotive headlamp without involving the use of 'fluid mechanics and structure mechanics', were investigated for practical use. In order to predict natural convection inside a headlamp, CFD has been examined for practical use and the following conclusions are given: 'SHT method' was developed newly, in order to predict temperature on the surface of the plastic parts inside the headlamp. Compared with the conventional method involving 'the couple of the fluid mechanics and the structure mechanics'; quadratic tetrahedron elements were used practically to generate the mesh based on CAD data, because, inner structure of a headlamp is complicated; in order to evaluate problems in generating the mesh quantitatively, hexa mesh and tetra mesh were examined by using the standard experimental setup; reliability of the calculation was evaluated by velocity measurement results (PIV) and temperature measurement results (thermocouples), and then, the calculation errors were also evaluated; 'SHT method' was applied to an actual headlamp, and it was found that temperature on the surface of the plastic parts was predicted within +/- 10 Grad C accuracy.