Abstract: After briefly analyzing problems of the machine test equipments at present, this paper rebuilds a new welding machine test device, based on virtual instrument technology. Using LEM sensor voltage and current, sampling signal data with high speed data sample card woke in computer, applying software to process the date, acquiring RMS current and voltage according to original define, displaying the value data and waveform PC panel, this rebuilding device can accurately give not only the value of the current and voltage, but also the power,the power factor and the total harmony distortion. At the same time, the device can used to statistics and analyze real welding process.