The invention relates to a method for determining an integrated network loss rate in the UHV AC cross-regional electricity trading. The method includes fitting a curve relationship between integrated network loss rates and transmitting powers on the basis of theoretical calculations of the UHV AC transmission line loss, using a relational fitted curve between actual values of integrated network loss rates and transmitting powers calculated according to gateway power statistical data to perform geometrical average correction on the original curve, and making planned values of the integrated network loss rates to be closer to the actual values according to a method for determining UHV AC integrated network loss rates according to a correction curve function relation, which greatly increases fairness of the trading settlement. The method is simple and easy to implement with high accuracy, and applicable to planning and trading settlement of regular or real-time UHV AC electricity trading.