The invention discloses a bias seam method for a laminated iron core of a transformer. In the method, laminates which are sequentially arranged in each laminate group of the transformer are divided into an odd group and an even group, the seam position of each laminate in the odd group and the even group is arranged at the same slope, the seam positions of the second laminate and the fourth laminate are forwardly leaded or backwardly leaded, and the seam positions of first laminate, the third laminate and the fifth laminate are arranged with a certain space. The seam arrangement of the laminates of the transformer is between stagger seam and stepped seam, so that the transformer has integral mechanical strength and short-circuit resistance capability of the stagger seam mode while maintaining excellent no-load loss performance and lower noise of the stepped seam mode, and the integral performance of the transformer is improved.