The conventional methods of determining the dynamic resistance were mostly done by measuring the voltage and current at secondary side of transformer in resistance welding machines,in which the measuring set-up normally interferes with the movement of electrode,and the measuring precision is influenced by inductive noise caused by the high welding current.In this study,the dynamic resistance is determined by measuring the voltage at primary side and current at secondary side.This increases the accuracy of measurement because of higher signal-noise ratio,and allows to apply to in-process system without any wires connected to electrodes. The conventional methods of determining the dynamic resistance were mostly done by measuring the voltage and current at at secondary side of transformer in resistance welding machines, in which the measuring set-up normally interferes with the movement of electrode, and the measuring precision is influenced by inductive noise caused by the high welding current.In this study, the dynamic resistance is determined by measuring the voltage at primary side and current at secondary side. His increases the accuracy of measurement because of higher signal-noise ratio, and allows to apply to in -process system without any wires connected to electrodes.