Abstract: This paper proposed a new hybrid DC transmission system which makes the maximum utilization of the line commutation converter（LCC） and voltage source converter（VSC）, as well as the overhead lines and DC cables. In resource-rich areas, the LCC can be employed to convert the clean energy into the UHVDC electrical power. By using the high voltage overhead line, which is cheap, reliable and low power losses, the electrical power can be transmitted to the edge of the load center by the LCC, and part of the electrical power can be fed to the local power system. The remaining electrical power will be separately delivered to the load center by the DC cables or overhead lines, converted by the VSC and injected to the local power system. In this paper, the hybrid DC system math model and control strategy were discussed. Based on the simulation analysis, the typical transit characteristic, such as the start, dynamic performance communication failure, line faults, and AC fault were presented. The results show that the system can keep stable and have superior dynamic performance in the various transits.