A proposed thermal model is examined for a distribution transformer. A 2d simulation by a transient analysis in light of the Finite Element Method (FEM) was done to obtain the temperature distribution in the three phase transformer (250 KVA 11/.416 KV core type, mineral oil) using "ANSYS PROGRAM". Meanwhile, the effects of type of oil on HOST are investigated using the proposed model. To test the effect of nanoparticles on heat transfer process, the insulation oil was changed with Nanofluid; it has been used two types of Nano particles (CuO and Al2O3) with 0.5% as a volume concentration, where themaximum temperature reduced about (5%).The core material also has been changed from silicon steel to amorphous steel and caused a reduction in maximum temperature about (9.9%) in HV winding and change the interior angles from 90o to 135o, where the temperature distribution transformer is improved. The present model successfully accomplished for expecting the temperature distribution at any locations in the transformer when compared with practical measurement.