The application relates to a secondary battery and an assembly method thereof. The secondary battery comprises a secondary battery assembly, the secondary battery assembly comprises an electric cell assembly, a transfer conductor and an insulation plate, wherein the electric cell assembly comprises at least two electric cells arranged side by side, and each electric cell has a tab extending from the top surface of the electric cell. The transfer conductor is provided with a transfer conductor tab assembly part. The insulation plate is located between the electric cell assembly and the transfer conductor, and the insulation plate is provided with a plate tab matching part, wherein, the folded tab passes through the plate tab matching part of the base plate and the transfer conductor tab assembly part in turn, and then is welded with the transfer conductor. The secondary battery of the application features short tabs, good battery performance, high safety, high assembly efficiency and low cost.