The invention relates to a DC power transmission converter valve testing device and a testing method thereof and specifically to a high-voltage DC power transmission converter valve fault current testing device and a testing method thereof. The testing device comprises a high-voltage loop, a tested valve, and a DC loop which are successively connected in parallel. A fault current loop is connected with the high-voltage loop and the tested valve Vt. The testing method of the testing device is also provided. The testing device fully utilizes a superposed loop principle, improves utilization efficiency, and saves cost. The testing device may achieve a large-range adjustment of the fault current, satisfies the fault current test requirements of a conventional high-voltage DC engineering converter valve and an extra-high voltage DC engineering converter valve, and is good in universality. The testing method fully utilizes the superposed loop principle and enables a fault current strength I2t to be more close to a real operation condition when the fault current is equal to a real engineering current peak value.