Measuring heavy fault current un-distortedly is essentially important in the research on the electric characteristic of vacuum circuit breakers in high-voltage switchgear. Based on non-contacting method for current measurement in high voltage environment， this paper proposes an electronic current transformer using the straight-part coil as the sensing part near high voltage conductor to measure fault current. Prototype has been made based on the analysis on structure and error characteristic. Test results show that the sensing part has a ratio error of less than -1.05% within±5mm flat error and -1.29% within±5° rotated error during installation. The approach is validated with the results of long-term field operation.