Transmission operating loss is an important factor affecting the economy of the whole transmission system. According to the equivalent mathematical model of AC transmission system, the UHV AC and EHV AC transmission schemes are constructed to meet the same transmission capacity, and the loss rate of each transmission scheme is calculated. It analyzes the influence of the change of the nominal transmission capacity, transmission distance and load rate on the loss rate of each transmission scheme. The results show that the characteristics of UHV in various situations can greatly reduce the operating loss, especially for long distance and high load rate. The conclusions can be used to the technical and economic comparison of UHV and EHV, especially for searching for the respective economic zone and the transmission range of advantages.