With the improvement of the automation level of substation and the popularization of intelligentization, the security of equipment operation has been paid more and more attention.The problem of the deficiency in discharged live detection technology of transformer bushing tap is becoming more and more obvious. Aiming at the present problem, the paper developed a set of portable bushing up discharge live detection device which is ease of operation and tour-inspection suited. The device adopts the method of real-time non-contact detection and discharge singals, and detect faults through observing signal waveform, size of energy discharge and spectrum changes, so as to detect faults accurately and timely. In this paper, the hardware structure and software key principle of the device were described in detail. At the same time, a comprehensive method for the diagnosis of the test tap to discharge is studied. It is of great significance to provide technical support for the electric inspection of discharge defect and ensure the safe and stable operation of transformer.