A few-mode fiber for space division multiplexing is proposed. By adopting a rectangular-assistant ring-core refractive index profile structure, which is similar to an ancient coin pattern, the fiber can eliminate the spatial degeneracy between the mode groups LP_mn,a (m=0,1,2,…;n=1,2,3,…) and LP_mn,b in the conventional few-mode fiber, maintaining a low level birefringence characteristics. These characteristics can significantly reduce the application difficulty of this type of mode group in space division multiplexing. In the optimized structure proposed in this paper, the refractive index difference of LP_mn,a and LP_mn,b is in the range of (2.2-6.5)×10^-4 at 1550 nm, which is at the same level as the refractive index difference of adjacent modes. In addition, the polarization separation level of each mode is 10^-6 or below. The design goals of significant separation of spatial degeneracy and unseparated polarization degeneration are well achieved. The simulation analysis shows that the structure has good deformation tolerance for the machining process.