The electrode cap (EC) is a key component of resistance spot welding (RSW). In this study, EC materials of Cu-Cr-Zr copper alloy (CA), Al2O3 CA, and rare earth (RE) CA were used to study the composition, conductivity, microstructure, microhardness, and life span of the materials under the cyclic heat and stress. The research shows that the Al2O3 EC has high hardness and heat resistance because the Al2O3 particles are distributed in the grain boundary in spherical or ellipsoidal shape. It is especially suitable for thermoformed plates at high-current welding scenes. The Al2O3 and other intermetallic compounds are stable and tend to fragment and spheroidize under the cyclic heat and stress, which ensures a high deformation resistance and electrical conductivity. The material of the RE EC has the characteristics of a twin microstructure. Under the cyclic heat and stress, through multiple twin deformations and dislocation interweaving, the grains become smaller, accompanied by the precipitation of dispersed spherical intermetallic compounds. The hardness and deformation resistance were improved, and exhibited high electrical conductivity and interface corrosion resistance. The quality of the joint and the life of the EC can be improved. RE CA is more suitable for two-layer galvanized plate welding, with high welding quality, better corrosion resistance, and higher electrode life. A comparative study of the properties and life of Al2O3 EC and RE EC with the traditional CA EC Cu Cr–Zr provides a theoretical basis for the selection of EC materials based on the materials, plate thickness, and welding parameters.