Abstract: Current-carrying capacity is an important parameter of cable transmission lines, which has a significant impact on the transmission capacity of the cable lines. With the continuous development of society, higher requirements have been put forward for the transmission capacity of cable lines. In order to further enhance the transmission capacity of high-voltage cable lines, the 500kV power cables laid in power tunnels are taken as the research object. By installing water-cooled pipes in the power tunnels, methods to increase the current-carrying capacity of power cables are explored. The material of the water-cooled pipes arranged in the power tunnel and the installation position of the water-cooled pipes were studied by numerical simulation, and the effect of increasing the cable current-carrying capacity under different conditions was analyzed. The results show that installing water-cooled pipes in power tunnels can effectively increase the current-carrying capacity of power cables. At the same position, there is no significant difference in the effect of increasing the cable current-carrying capacity when water-cooled pipes are made of HDPE and galvanized steel pipes. The installation of water-cooling pipes at different positions has different effects on increasing the current-carrying capacity of cables. When the installation position of water-cooling pipes enters the high-temperature area around power cables, it can effectively remove the heat around the cables, and the effect of increasing the current-carrying capacity of the cables is the most obvious. Installing water-cooled pipes in power tunnels can effectively increase the current-carrying capacity of cables. When the transmission capacity of power cables laid in power tunnels still fails to meet the requirements, the method of adding water-cooled pipes in the tunnels can be attempted.