The invention belongs to the technical field of energy conservation of electrical power systems, and especially relates to a method for calculating efficiency of a 750 kV transformer related to loss of a reactive compensation apparatus. The invention comprises: establishing a comprehensive loss model of the 750 kV transformer, and constructing a calculation formula of loss of the 750 kV transformer body; determining a loss function of the reactive compensation apparatus at a low-voltage side according to a specific type of a compensation device; and determining the highest comprehensive efficiency of the 750 kV transformer and a corresponding exchange power of the transformer. The method for calculating efficiency of the 750 kV transformer related to loss of the reactive compensation apparatus can combine a formation feature of loss of the 750 kV transformer effectively, consider various loss types/various types of loss comprehensively, and be used to analyze a loss characteristic of the 750 kV transformer, which provides a more reasonable basis for economical operation of a 750 kV power grid.