Abstract: A test method, based on the three-electrode system under a thin-layer electrolyte, for determining the galvanic compatibilities of spacecraft dissimilar materials is proposed,to fulfill the needs of corrosion evaluation of the spacecraft launched from Wenchang Satellite Launch Center. A threeelectrode system under a thin-layer electrolyte was designed,and galvanic corrosion tests on five types of spacecraft materials were conducted under a temperature and humidity controlled thin-layer electrolyte.Results show that owing to the ohmic resistance and the polarization extent of anodic and cathodic metals,thin-layer electrolytes are more favored environmental conditions for assessing the galvanic compatibilities of spacecraft dissimilar materials than aqueous solutions,and there is a strong correlation between galvanic current densities and environmental conditions. This work suggests that the three-electrode system under a temperature and humidity controlled thin-layer electrolyte and the criteria of galvanic current density should be used to assess the galvanic compatibilities of spacecraft dissimilar materials.