Abstract: In response to the problem of low efficiency in calculating transient temperature rise of oil immersed power transformers, this paper proposes POD-αATS reduced order adaptive variable step size transient calculation method. First, the article briefly derives the finite element discrete equation for calculating the transient temperature rise of transformer windings. Next, the proper orthogonal decomposition (POD) order reduction algorithm is adopted to improve the problems of excessive number of conditions and equation orders in traditional transient calculations. Meanwhile, for the time step selection problem in transient calculations, this paper proposes a method suitable for nonlinear problems α ATS (adaptive time stepping based on α factor, αATS) variable step size strategy. Then, in order to verify the effectiveness of the method, this paper establishes a two-dimensional eight zone numerical calculation model based on the basic structure of the 110 kV oil-immersed power transformer winding, and compares the calculation results with the temperature rise experimental results based on the 110 kV winding. The numerical calculation and experimental results show that the accuracy of the proposed algorithm is almost the same as that of the full order fixed step algorithm in the flow field and temperature field, the efficiency of flow field calculation is improved by about 45 times, and the efficiency of temperature field calculation is improved by about 38 times, significantly improving the calculation speed. This has also been verified in temperature rise experiments, which fully demonstrates the accuracy, efficiency, and certain engineering practicality of the algorithm proposed in this paper.