Accurate calculation of the hot spot temperature (HST) in transformer windings is essential for ensuring the reliable operation of the transformer. However, current methods have limitations in real-time prediction of winding HST leading to inadequate performance under complex operating conditions. This paper establishes a simulation model of the thermal field of transformer based on the dynamic mode decomposition (DMD) method, extracts snapshot matrices at different moments, and calculates the HST of the thermal field of the transformer under the dominant modes to achieve rapid HST calculation. The results show that: 1) When the selected modal energy is > 90%, most of the physical field information is included. 2) In thermal field simulation, by selecting the first 10 modes to reconstruct the thermal field data, the calculation time is reduced from 391 s in COMSOL simulation to 120.5 s, improving calculation efficiency by 3.24 times, with a calculation error of 1.06%. The research results of this paper provide a theoretical basis for real-time prediction of transformer winding HST.