To improve the efficiency of setting calculation for traveling wave protection, this paper studies the extreme connection modes of VSC-HVDC grids. Firstly, the extreme values of characteristic quantities required for setting calculation are clarified based on the setting calculation principle of a typical traveling wave protection scheme. The four most typical connection modes are then selected by referring to the standard connection modes of the Zhangbei VSC-HVDC grid. By deducing and comparing the expressions of each characteristic quantity under these four connection modes, the required extreme connection modes are pre-determined. In this way, the simulation workload of setting calculation can be greatly reduced. Finally, the correctness of the determined extreme connection modes is verified in PSCAD/EMTDC. The setting calculation for the simulation model are also conducted using these determined extreme connection modes. The results demonstrate the significance of this research in improving the efficiency of setting calculation.