The Li-CO2 battery captures CO2 gas and converts it into electricity, which can not only alleviate the greenhouse effect, but also provide a higher theoretical energy density, which has attracted wide attention from researchers. However, Li-CO2 batteries still face some thorny problems, such as high overpotential and poor cycle life. Electrocatalysts that efficiently promote the reduction of CO2 and the decomposition of discharge products play a key role in Li-CO2. Using hydrated ruthenium trichloride solution as the precursor, ruthenium dioxide (RuO2) nanoparticles were uniformly loaded on the carbon nanotube (CNT) substrate by a simple hydrothermal method, and the ruthenium dioxide nanoparticles were successfully prepared with uniform dispersion and RuO2-CNT catalytic cathode with three-dimensional porous structure. Under the dual action of the three-dimensional porous structure formed by cross-linked carbon nanotubes and the high-efficiency catalytic activity of RuO2 nanoparticles, the discharge capacity and cycle performance of the Li-CO2 battery are significantly improved. At a current density of 100 mA·g-1, the first discharge specific capacity can reach 1 912 mAh·g-1. In addition, under the conditions of a current density of 100 mA·g-1 and a constant capacity of 500 mAh·g-1, it can be cycled stably for 120 cycles. It provides a new idea for the design and preparation of Li-CO2 battery catalytic cathode.