Abstract: As an important component of the overall loss of high-frequency transformers, winding loss is a key parameter that affects the volume, efficiency, and temperature rise of magnetic components. The complex three-dimensional twisted structure of the Litz-wire can effectively reduce the additional losses caused by high-frequency skin effect and proximity effect, and it is widely used in high-frequency transformers. However, the eddy current distribution inside the Litz-wire winding is extremely complex, and existing analytical calculation methods require more simplification and approximation of the model, making it difficult to accurately characterize the high-frequency eddy current effect of the Litz-wire winding. Numerical calculation methods require fine-grained modeling of the Litz-wire, resulting in severe consumption of computational resources. Therefore, how to accurately and quickly calculate the winding losses of the Litz-wire is of great significance for the optimization design of high-frequency magnetic components. Based on the analysis of the winding loss mechanism of Litz-wire and the analytical method and the finite element numerical method, a 3D fast calculation model of winding loss is established considering the winding end effect and the circular Litz-wire stranded structure. Finally, for two different transformer models with different Litz-wire windings, detailed experimental research and comparative analysis are carried out from the point of view of calculation accuracy and calculation cost. The results indicate that the model proposed in this article achieves accurate and efficient calculation of circular Litz-wire winding losses over a wide frequency range.