A hybrid DC converter with a series Line-Commutated Converter (LCC) and a Voltage Source Converter (VSC) has advantages in avoiding commutation failure and blocking the DC fault. In this paper, the operation mode, control strategies, protection principle of the VSC, effect of commutation failure and process of the DC line restart are presented. The hybrid HVDC system constituted by the hybrid DC converters, which overcomes some drawbacks of the LCC HVDC and the VSC HVDC, has more advantages for fault toleration. For AC system faults in the inverter, the VSC can supply the constant or higher voltage to suppress the increasing direct current and to lower the effect of commutation failure in the LCC. For DC grid faults, the LCC in the inverter can block the large reversing fault direct current caused by the VSC, with DC line fault restart capability. In addition, the VSC can supply a large amount of reactive power for the LCC, thus reducing the converter station reactive equipment configuration. This work is supported by the Youth Science Fund of National Natural Science Foundation of China (No. 51607042).