Abstract: Direct current spot welder with secondary rectification is more and more widely used in the industry because of its high power factor and balanced load on three phases. In spot welding of important assemblies, the visualization of quality control is helpful to the online welding quality evaluation. This paper discuses the soft ware realization of serial communication and welding current waveform display with VB6.0 on Personal computer, analyzes resulted waveforms such as that of the typical single pulse, typical dual pulse, single pulse per two cycles, and the effect of constant current control while power voltage increasing or decrea-sing. These waveforms directly explain the major characteristics and advantages of the three-phase secondary rectification. The developed system has been successfully used in the spot welding of aluminum frames of a large sized rocket.The welding current waveform displaying and filing system have become an important auxiliary quality evaluation measure for welding operators and quality inspectors.