The present disclosure proposes a secondary battery and welding method thereof. The secondary battery comprising a top cover, a pole, a cell and a transfer sheet, wherein the pole comprising a first pole, which being provided in the top cover; the cell comprising a first cell, the first cell leading out a first tab and a second tab with opposite polarity; the transfer sheet comprising a first transfer sheet, the first transfer sheet electrically connecting the first tab to the first pole; wherein the first transfer sheet having a first surface and a second surface oppositely, the first tab and the first transfer sheet being connected in any of the following two ways: a part of tabs of the first tab being connected to the first surface, other part of tabs of the first tab being connected to the second surface, the first transfer sheet being located between the part of tabs of the first tab and the other part of tabs of the first tab, or, all tabs of the first tab being connected to the first surface of the first transfer sheet.