In transmission line equations with distributed parameters, corona power losses are represented as conduc- tivity, i.e. corona losses considered as a function of the line voltage squared. On the other hand, valid corona power losses are 4-8 degree functions from voltage. Therefore, extra high voltage transmission line equations with the distributed parameters have methodical errors. Methodical errors of extra high voltage transmission line operation mode parame- ters modeling are estimated. The method of modeling extra high voltage transmission line operation mode taking into account actual corona-loss characteristics is offered. The cascade-connected scheme is used for increasing the accuracy of modeling extra high voltage transmission line operation modes in this method. In the offered method, corona power losses consist of two components. The first component is represented as conductivity. The second component is represented in the form of additional loading. Using the proposed method allows incorporation of phasor measurements of electrical parameters into the calculations. The accuracy of modeling using information received from the phasor measurement units is investigated. The software for modeling an extra high voltage transmission line's operation mode is developed on the basis of the proposed method. Results of modeling for a 750 kV extra high voltage transmission line are represented.