This paper presented the charcteristic of the thermal transfer in a 50[kVA] cast-resin dry type transformer. The conductivity of the primary winding composed were a Plenty of epoxy-resin ard a little of Cu was determined by that rating. Otherwise the conductivity of the secondary winding composed of a plenty of Cu and a little of epoxy-resin was determined by comparing the data of analysis using FEM method with those of temperature tests of the prototype cast-resin transformer. Based on the reults of the physical characteristics and the simulation by commercial using FEM method we established the prototype Model for this test. According to that Model, an analysis on variation of the temperature was discussed as a function of ambient temperature and velocities in the 50[kVA] cast-resin dry type transformer.