This paper addresses the problem that the existing power measurement methods cannot accurately distinguish between linear and nonlinear loads, the emission and absorption of harmonic power, and the magnitude of background harmonics in complex systems with harmonic sources in the extra-high voltage transmission gateway metering system. This paper proposes a harmonic source identification technique based on the partial least squares regression model, and based on this method, a new and more reasonable metering model is proposed, which is able to distinguish various types of power types, so that when harmonics are present in the system, each department can take its own responsibility to achieve the purpose of reasonable metering, with clear rewards and penalties.