The application of virtual instrument technology

which is used in the on-line partial discharge detecting system for power transformer is introduced in this article. The hardware structure and its function are analyzed. With the control function and the powerful digital processing function

the periphery hardware circuit and the data acquisition mode can be controlled efficiently

and the methods such as digital filter and polarity identification have been applied to signals

which can ensure the measurement accuracy. The 3D and 2D graph representing the characters of partial discharge and the tendency graph representing the increasing of the level of partial discharge have also been made by the statistics analyzing method.