The application provides a variable-frequency power transmission system, including a new energy power generation base for supplying electrical energy to an AC grid, and operating in a constant-voltageconstant-frequency or constant-voltage variable-frequency mode based on environmental conditions including meteorology, environment and distance; a first isolation device connected to the new energypower generation base; a second isolation device connected to the AC grid; an AC-AC frequency conversion device having an input end connected to the first isolation device and having an output end connected to the second isolation device; and a power transmission cable connected with the new energy power generation base and the first isolation device. The variable-frequency power transmission system can reform the power supply in remote areas or between multiple islands, can increase a transmission capacity, reduce a line loss, increase a transmission distance, save transformation cost, reduceconstruction difficulty, and uses the first isolation device and the second isolation device for electrical isolation of the low-frequency discharge in a power transmission line to ensure the safetyof low-frequency power transmission.