An on-line partial discharge detection instrument for SF6-insulated switchgear using wireless communication technology is proposed. Two major parts is divided for the developed instrument. One is the remote wireless monitoring with on-line measurement unit that could be placed permanently onto the SF6-insulated switchgear equipment so as to measure the partial discharge signal from an ultrasonic sensor. The other is the server analysis and calculation unit. It is mainly composed of an industry computer containing a wireless module. The function of this unit is to collect, analyze and store the ultrasound signal captured from each remote monitoring unit, and to perform software-based signal noise and interference reduction. Through feature extraction of the original ultrasound signal, a digitalized assessment and recognition system of the state of insulation could be created.