Abstract: With the application of overhead lines in DC transmission engineering and the gradual construction of multi-terminal DC power grids, the half bridge-full bridge sub-module hybrid modular multilevel converter (MMC) has a broad application prospect, with its loss calculation having great engineering significance. For the half bridge-full bridge sub-module hybrid MMC to be added into the control unit with the secondary circulation current suppression and the triple frequency voltage injection, its working principle and modulation strategies are described, and the loss of the converter valve is classified and the calculation method is given: the on-state loss is calculated in sections according to the current direction of the bridge arm; the switching loss is calculated in sections according to the current direction and the voltage variation of the bridge arm. The simulation in PSCAD/EMTDC verifies the correctness of the half bridge-full bridge sub-module hybrid MMC valve loss analysis. The calculation and simulation results show that the valve loss of the half bridge-full bridge sub-module hybrid MMC is positively correlated with the proportion of the full-bridge sub-modules, and is affected by the power factor Angle and the modulation ratio. That is, within the allowable range, the closer the power factor Angle is to zero, the lower the loss is; and the higher the modulation ratio, the lower the loss