In this research, a static electric contact tester with a vacuum system is used to inverstigate the efedts of experimental parameters, such as air pressure, input voltage and current, contact material, and the gap between the contacts, on the electric-arc characteristics and the erosion debris type for the electric contacts of silver (Ag). The experiments are conducted under various experiment parameters, and the erosion debris is collected. After each experiment, the erosion debris will be calculated and observed to investigate the difference between erosion particles under various experiment conditions. Moreover, according to the results of the metallic phase and gaseous phase arc duration and the erosion particle type under various air pressures and the gaps, the electric-arc criterion and the erosion mechanism of DC electrical contacts will be established to provide the domestic electrical contact manufacture in improving the research and development technique of electrical contacts, and the design reference of super precision environment¡Xclean room