The invention provides a self-adaptive differential current calculating method for tap position adjustment of an extra-high voltage regulating transformer. On the basis of a special electrical structure of the extra-high voltage transformer, real-time running tap position information of the voltage regulating transformer is obtained through an indirect calculating method and introduced into differential protection of the voltage regulating transformer, and differential current is accurately and reliably amended. The self-adaptive differential current calculating method for tap position adjustment of the extra-high voltage regulating transformer solves the problems that the extra-high voltage transformer can not obtain real-time tap position information in the field actual engineering, and as the voltage regulating range of the voltage regulating transformer is very large, differential current led into a protection device differs largely under different tap positions, improves flexibility of differential protection when the voltage regulating transformer has a fault, not only solves the difficult problems in the actual engineering, but also has actual significance of improving the reliability of differential protection of the extra-high voltage regulating transformer, ensuring accurate and reliable actions and the like.