The invention discloses a cathode carbon block structure capable of reducing horizontal current in molten cathode aluminum in an aluminum electrolysis cell, and belongs to the technical field of aluminum electrolysis. The cathode carbon block structure comprises a cathode carbon block and a cathode steel bar, the longitudinal section of the top of the cathode carbon block has reverse trapezoidal structure or reverse triangular structure, the top of the cathode carbon block is divided into two or three sections, and the vertical height difference between two ends of an inclined section is 1 to 6 percent of the axial length of the cathode carbon block. According to the cathode carbon block structure, the electrolysis current released from the electrode during electrolysis in the electrolysis cell in the vertical direction vertically enters the cathode carbon block through the molten aluminum, so that the purpose of eliminating or greatly reducing the horizontal current in the molten cathode aluminum in the electrolysis cell is fulfilled. The cathode carbon block structure is suitable for an electrolysis cell without a lug boss on the surface of the cathode carbon block, a special-shaped cathode structural electrolysis cell with a lug boss on the surface of the cathode carbon block and a cathode structural electrolysis cell with a TiB2/C composite coating on the surface of the cathode.