Line commutated converter based HVDC (LCC-HVDC) is better than AC transmission in power transmission characteristic, self-defense capability in line fault, overloading capability, but it can’t supply the weak AC system and passive network. Voltage source converter based HVDC (VSC-HVDC) can supply the passive network, but the cost of its investment is high because of the limitation of power electronics technology. This paper proposes a new novel hybrid HVDC (H-HVDC) transmission system combining the advantages of both sides. The rectifier side of the H-HVDC is that two 6-pulse LCC connect a AC network, and the inverter is that three-phase two level VSC connect a passive network. On this basis, its steady-state mathematical model, start-up characteristic, steady-state and transient characteristics, monopole block are deduced. Simulation results show that this H-HVDC system can supply the passive network with high stability, which provides a theoretical foundation for further development of the future in hybrid HVDC.