Oil - immersed transformers play a vital role in power systems and are one of the indispensable main equipment in power transmission and distribution links. Reducing the losses of oil - immersed transformers can not only improve energy utilization efficiency, but also reduce operating costs, which is of great significance for achieving energy - saving and emission - reduction targets. Among the many factors affecting transformer losses, the structural parameters of the core play a crucial role. This paper analyzes the principle and losses of 10kV oil - immersed transformers, builds models of cores and windings with different structures, and compares and analyzes the no - load losses and load losses of cores and windings with different structures. Finally, it compares and analyzes the hot - spot temperature rise and oil velocity of transformers with different structures. The research results provide a reference direction for the energy - saving design of transformers.