Abstract: Epoxy resin sealing high frequency transformer (ERS-HFT) uses epoxy resin as the insulation material, greatly reducing the volumes of the equipment. As it is difficult to dissipate the internal heat in the ERS-HFT due to the poor thermal conductivity of the epoxy resin, a heat dissipation method is proposed by adding a heat dissipation water pipe between the high-frequency transformer core and the low-voltage winding in this paper in order to effectively reduce the operating temperature of the ERS-HFT. Based on the 10kV ERS-HFT, both the core loss and the winding loss are calculated, and the loss test platform is built. The comparison between the calculation results and the test results proves the accuracy of the loss calculation method. With the loss of ERS-HFT as a heat source, the finite element simulation model of temperature field is established. The influence laws of various factors on water cooling and heat dissipation effects are analyzed, including water flow rates, water pipe materials, thermal conductivity of epoxy resin, etc. The temperature rise test of the 10kHz/200kVA ERS-HFT is carried out with the error of only 2.7% between the test results and that of the finite element model, which verifies the accuracy of the finite element model and the effectiveness of the heat dissipation method.