High-Frequency Transformer (HFT) is a core component of power electronic transformers and dual-active-bridge DC-DC converters. The distribution characteristics of its temperature and stress fields are crucial for system reliability and environmental friendliness. In this study, a 5kHz/10kVA HFT was analyzed using finite element simulation software. A full-chain multiphysics coupling simulation covering electromagnetic, fluid, thermal, structural, and acoustic domains was conducted to obtain the distribution patterns of electromagnetic, temperature, stress, and other multiphysics fields under nonsinusoidal excitation. The results reveal that the core loss of the high-frequency transformer is 52.7W, with high-voltage and low-voltage winding losses of 13.23 and 3.01W, respectively. The maximum magnetic flux density under sinusoidal excitation reached 0.746T, while under square wave excitation it reached 0.923T. The hotspot temperature was located approximately two-thirds along the core column at 115℃, with the lowest temperature recorded at 92.3℃ beneath the high-voltage winding. Forced air cooling demonstrates significant cooling efficiency below 4m/s wind speed, with cooling rates slowing thereafter. At 4m/s wind speed, core stress amplitudes under sinusoidal and square wave excitation were 2.81×106 and 3.65×106N/m2, respectively, with sound pressure level amplitudes of 78.1 and 94.9dB. When further considering the effect of thermal stress, under natural air cooling and square wave excitation, the core stress rises to 3.92×106N/m2, the vibration acceleration increases to 64.3m/s2, and the maximum sound pressure level reaches 97.3dB, representing increases of 7.4%, 6.8%, and 2.4dB, respectively, compared with the forced air cooling condition. Owing to its rich harmonic content, square wave excitation leads to significantly greater deformation, stress and noise than sinusoidal excitation, while thermal stress, as a secondary factor, further exacerbates vibration and noise levels. Through multiphysics simulation, the influence mechanism of waveform excitation and thermal stress on the comprehensive performance of transformers is revealed, providing a theoretical basis for multi-objective optimization of high-frequency transformers.