Discharging state is usually detected by measuring the average voltage of interelectrode path in microelectrical discharge machining (Micro-EDM). The principle and circuit are simple and effective for normal EDM. But, according to its principle, the detection sensitivity and the threshold voltage will be great different due to different pulse parameters, especially when the pulse width is narrow and pulse duty ratio is small. Thus, the average voltage detection method is lacking in adaptability. A novel method to detect discharging state was presented.The variance of interelectrode voltage, which was led by variance of impedance, was used to judge the discharging state. By this means, when the detection circuit was fixed, the detection sensitivity and the accuracy of threshold voltage was not varied according to different pulse parameters. Consequently, the novel method was of good adaptability in realistic machining situation when different groups of pulse parameters were needed for different processing requirements. The basic circuit detecting interelectrode voltage was built based on the variance of impedance. Experiments were done to testify the detection principle. Experimental results show that different discharging states can be distinguished by the detection circuit and the effectiveness of the method is proved.