The surface characteristics of reaction-bonded SiC (RB-SiC) ceramic with Electrical Discharge Diamond Grinding (EDDG) were explored. Three kinds of processes of EDDG, Electrical Discharge Grinding (EDG) and Conventional Grinding (CG) were taken into the experiments of RB-SiC grinding. Then the surface roughnesses of the RB-SiC were measured with a laser scanning confocal microscope, and their surface morphologies and micro-cracks were observed with a scan electron microscopy. The grinding characteristics of the RB-SiC with EDDG were analyzed and compared to that with other two methods. The results show that the surface roughness value of RB-SiC is 0.214 9 μm with the EDDG, which is better than that with EDG but slightly poorer than 0.1956 μm with the CG. For the surface morphologies of the RB-SiC, it shows obvious discontinuous scratches with the CG, and is mainly composed of discharge craters with the EDG machining. However, both scratches and discharge craters are existed on the machined surface with the EDDG. Moreover, the grinding cracks and grain boundary cracks are found on CG surface and only hot cracks exist on the EDG surface. But the micro-cracks on EDDG surface are divided into grinding cracks and hot cracks, and the latter can be ground with diamond grits. With the investigation of comparative experiments, the results show that different machined surface characteristics of RB-SiC ceramic with EDDG process from that with EDG and CG processes.