The invention provides a power battery and a sealing nail thereof as well as a welding method of the sealing nail. The sealing nail comprises a main body and a flange, wherein the main body takes on a frustum shape, and the top of the main body is protruded outwards along a circumference. The welding method comprises the following steps of enabling the main body of the sealing nail to be contained in a containing groove arranged at a liquid injecting hole of a top cover of the power battery, enabling the flange of the sealing nail to be carried on a carrying surface of the top cover, and enabling the sealing nail and the top cover to be combined together by adopting laser full-penetration welding. The welding efficiency can be greatly improved.