Because of strong current, friction and arcing, electrical contact ablation occurs in the transmitting process of electromagnetic railgun, which is also one key issue in application. In this paper, an experimental apparatus is designed to detect electromagnetic railgun armature contacts ablation. Energy dispersive X-ray, scanning electron microscopy, high-resolution camera and rogowski coil are used to measure mass loss, volume change, the ablation layer analysis, the element distribution on ablation layer section and the electrical contact analysis. Experimental results show that the input current and the contact pressure between electrodes are the major factors contributing to the ablation volume loss and mass loss. It is also showed that as a sliding electrode, the aluminum armature ablates more seriously during launch.