Abstract: A measuring system of dynamic resistance was developed to research on the resistance microwelding (RMW) process of insulated copper wire. The testing system is mainly composed of a PC, data acquisition card, digital trigger circuit and current sensor. The change regulation is concluded by measuring the dynamic resistance combining the analysis of faying surface by scanning electron microscopy and energy dispersive spectroscopy. The results show that the dynamic resistance is a monotonously decreasing curve due to lack of metal liquid or nugget formation; dynamic resistance manifests as disappearance of film resistance, decrease of constriction resistance and increase of bulk resistance. the dynamic resistance finally reaches an equilibrium state and shows an approximate level. A wave crest will appear when surface splash occurred. This peak characteristic can be used as the basis of weld quality monitoring.