Abstract: Using the Graphics Language-based virtual instruments developing tool LabVIEW,this paper develops a virtual instrument-dada acquisition and weld defects analysis in resistance spot welding system which has friendly interface and is easy to operate.The system realizes real time data acquisition in the aluminum resistance spot welding process,data transfer and storage,waveform display and data processing.Furthermore,it extracts characteristic information of evaluating weld defects of aluminum resistance spot welding.Based on the sufficiently study of the acquired data,this paper builds an algorithm of judging splash according to the slope coefficient of the voltage waveform and an algorithm of judging loose weld according to the energy.The algorithms built in this paper have been proved accurate.