The invention relates to a low-voltage arc starting and gap distance adjustable power-frequency freewheeling test apparatus. The test apparatus comprises an impact voltage generator system, a voltage measuring system, a Rogowski coil, a suspension insulator, a gapless segment of a lightning arrester, an upper spherical electrode, a lower spherical electrode, an arc ignition fuse and a power-frequency test power supply system. The arc ignition fuse is added to an air gap between the upper and lower spherical electrodes, and influence of impact voltage on a power frequency side power supply device is reduced substantially. The upper and lower spherical electrodes are fixed to the suspension insulator via holt hoop iron fittings, and the gap distance can be adjusted freely. The test method of the test apparatus comprises that the gap between the upper and lower spherical electrodes is adjusted, the arc ignition fuse is mounted, a power frequency voltage is output, an impact voltage is output, 5 tests are carried out, the gap distance is changed, test results are evaluated, and a most ideal gap distance design is changed. According to the test apparatus and method, the test period is shortened, the test efficiency is improved, the test strictness is enhanced, and the test accuracy is ensured effectively.