Up to now there has been no special monitoring equipment or platform for the energy efficiency measurement of large power rectifier system. For this reason, a new method of energy efficiency measurement of large power rectifier system based on the fiber optic Ethernet communication was presented. In order to prove the advantages of the new method, this paper made a comprehensive and comparative study of the measuring principles, and the analytical method of energy efficiency. The method of indirect inversion of heavy direct current proves to be correct and can be well applied in practical projects through simulation and experiments. Finally, by combining with engineering practice, the specific implementation process of the new analytical method of energy efficiency was described. The project case indicates that the efficiency analytic method can correctly calculate the efficiency of the power-supply system of the industrial rectifier system, and can provide a proof of improving the efficiency of the equipments and saving the energy of the system.