Compared with high temperature superconducting (HTS) ac cable, HTS dc cable has the advantages of large transmission capacity, low ac loss and strong controllability. Self-shielded HTS dc cables with different current directions in adjacent layers can reduce the magnetic field interaction between layers, so as to increase the critical current of the cables and reduce ripple loss. In this paper, a novel self-shielded dc cable is proposed, which is made of REBCO tapes with different widths. The magnetic field distribution, ac ripple loss of the novel cable and Ampere force are studied based on T-A formula. The results show that the wider outer tapes can counteract the magnetic field in the inner tapes, and the novel self-shielded dc cable has smaller magnetic field between layers, lower ripple loss and smaller Ampere force than the previous self-shielded dc cable made by tapes with the same width. This novel self-shielding structure provides a new idea for the design of dc cable for large dc applications.