Due to its good wettability to molten aluminum and good corrosion resistance to the molten electrolyte, TiB2 is a promising cathode material. Recently, a number of studies on TiB2-C composite cathode materials have been undertaken by researchers. Yet, the mechanism of TiB2 reducing sodium and electrolyte penetration is reported scarcely. In order to understand the effect of TiB2 on the performance of cathode materials for aluminum electrolysis, TiB2-C composite cathode materials were prepared by the hot press sintering process, and experimental investigation of sodium expansion of cathode samples was conducted in laboratory aluminum electrolysis cells. By virtue of detailed SEM, TEM, and XRD analyses, the interfacial behavior between TiB2-C composite material and the substrate, the effect of TiC on the performance of the cathode material, and sodium penetration were investigated elaborately. The results showed that TiC generated in the process of firing can increase the degree of graphitization and coherence length of La by converting the disordered carbon into graphite crystals during aluminum electrolysis. This catalysis process, which was called dissolution-precipitation mechanism, can improve the performance of cathode materials and reduce the penetration of electrolytes and sodium to the cathode. The electrical resistivity with TiB2-C composite cathode was 55.6 μΩ?m at 950℃, and that with the carbon cathode was 96.7 μΩ?m applied on the same temperature. As a result, the cathode voltage drop can be effectively reduced by using a TiB2-C composite cathode, which reduced energy consumption in production. The composition and structure of the cathode were changed in a gradient by inserting a transition layer so that the properties and functions of the cathode also were changed in a gradient along the gradient direction. Generally, cracking would initiate and propagate between the composite layer and carbon base because of a large mismatch of their thermal expansions. But the interface bonding between the TiB2-C composite and the substrate was significantly improved by inserting a transition layer, which can remarkably decrease sodium penetration. This work is useful for increasing the service life of cathodes and reducing the energy consumption of aluminum electrolysis.