Aiming at the problem that the output current and voltage of the electric vehicle charging pile show the fast-changing characteristics of “randomness, volatility and time-varying”, which leads to the problem of large out-of-tolerance of electric energy metering, a random signal mathematical model of the fast-changing DC current and voltage of the charging pile is established, and its time-frequency domain characterization model is established. A fast-changing waveform mode extraction method is proposed, and 12 fast-changing DC waveform modes of 6 categories are extracted. A mathematical model of eight characteristic parameters in the amplitude domain is proposed and constructed to characterize the current and voltage characteristics that affect the energy metering. The typical characteristic parameters and important characteristics are extracted. The value and characteristics of the characteristic parameter can provide a theoretical basis for formulating the test and evaluation test conditions for the dynamic error of the DC electricity meter.