As an important power equipment in the operation of power systems, oil – immersed iron – core reactors can compensate for the reactive power and capacitive current of power lines, suppress the voltage rise at the end of the lines, and meet the development requirements of China’s power transportation towards UHV and long – distance power transmission. However, during the operation, the reactors need to withstand lightning over – voltages and switching over – voltage impacts, so more accurate wave – process calculations for the reactor windings are required. Most traditional wave – process analyses use the equivalent method of two – turn or multi – turn windings for wave – process calculations, lacking the analysis of turn – level voltage distribution. In this paper, a single – phase reactor model is constructed, a turn – level equivalent circuit model and a capacitance calculation method suitable for large – scale windings are proposed, and the turn – level voltage distribution and main insulation voltage distribution of the reactor are obtained, providing a strong basis for the future optimization of the reactor’s insulation structure and over – voltage analysis.