Abstract: This paper introdces an electrode displacement monitoring system used in the resistance spot welding,composed of an LS type enclosed grating displacement transducer for dynamic measurments and a microcomputer measuring Unit.The experimental results,obtained under various welding processes and conditions,have shown that this system,characterized by its high speed and high accuracy,is capable of determining electrode displacements in the spot welding easily and reliably,and,therefore,is suitable to realize quality control in the practices.