Abstract: With the development of flexible DC grid, its boundary structure will be changed from "bounded DC grid" to "non-bounded DC grid". If the protection principle can be suitable for both boundary structures as much as possible, the complexity of protection verification and the economy of protection application can be greatly reduced when the grid structure changes. In order to improve the applicability of line traveling wave protection to different boundary structures, this paper proposes a novel traveling wave protection scheme. The protection scheme is mainly based on the FCINP. Based on the distance and boundary characteristics of FCINP under different boundary structure grids, the fault identification performance of the protection can be effectively improved under both bounded and non-bounded grids, thus improving the applicability of the protection. The performance of the proposed protection is verified in a PSCAD/EMTDC DC grid simulation model.