Abstract: Corona phenomenon of conductor is the electrical phenomenon that the electric field intensity of conductor surface is higher than that of surrounding medium, which is related to the spatial structure of conductor, voltage, atmospheric environment and other factors. The accurate measurement of the corona onset voltage can optimize the structure of the conductor and its electric field, reduce the corona loss, and improve the electrical strength. Based on the analysis of the process of space charge generated by corona and its distortion effect on electric field, a method of space charge detection around the conductor was proposed. By the voltage division mode of the stray capacitance between the conductor and the sensing electrode and the sampling capacitor, the rule that the corona space charge affects the induced voltage waveform under AC voltage was analyzed. The corona onset voltage of conductor was calculated by the method of feature extraction. The simulation experiment platform of conductor AC corona discharge was built to verify the validity of this method.