A back-back HVDC interconnector project is under construction at Luxi, Yunnan Province, China. One of two HVDC links of the project is rated 1000 MW using VSC-HVDC technology. The secondary side of converter transformer of VSC-HVDC is grounding through a 5kΩ resistor. The maximum steady-state loss(MSL) of the grounding resistor determines size and thermal designing of the resistor, meanwhile influences the thermal overload protection setting. In this paper, steady-state loss of grounding resistor under different operation modes is analyzed. It can be concluded that MSL appears at converter blocking state. Then, a theoretical calculation method of MSL based on energy conservation is proposed. It is shown that the proposed method is simple in calculation and clear in principle. The proposed method also reveals the influence factor of MSL, which provides ideas for reducing MSL. Finally, by compared with simulation results in PSCAD/EMTDC, the validity of the proposed method is verified.