Due to the problems of complex operating conditions and harsh working environment of wind turbine generators, in order to ensure the safe and stable operation of wind turbine generators, a method of early warning of electrical faults under full operating conditions of wind turbine generators based on digital twin technology is proposed. The method simulates the complex operation state of wind turbine by establishing a digital twin model of wind turbine to provide a reliable virtual environment for electrical fault early warning; the full operating wind speed is used as an input to monitor the three-phase current changes, and an enhanced nonlinear differential sequence distance (S-NDD) calculation method is proposed to construct the system state evaluation indexes in order to better retain the residual information between the digital twin and the actual system; For the complex and variable wind turbine operating conditions, an improved Chebyshev sliding window adaptive dynamic threshold (ICS-WADT) estimation method is proposed to set the system fault warning threshold. The results show that: the actual operation data of a 1.5MW doubly-fed wind turbine is verified to prove the high accuracy and effectiveness of the established digital twin model; at the same time, the monitoring of the three-phase current changes realizes the over-warning of the wind turbine electrical faults. It is concluded that this study provides an innovative solution to improve the reliability of wind turbines and reduce operation and maintenance costs.