A novel hybrid multi-terminal HVDC（MTDC） system， composed of line commutated thyristor current source converters（CSC） and GTO voltage source converters（VSC）， is proposed for the extension of the conventional HVDC system. To verify the feasibility of the proposed system， a simulation model for the hybrid three-terminal HVDC system is developed， which consists of a VSC terminal， a CSC rectifier， and a CSC inverter. Based on the developed MTDC system， two control schemes are proposed. The performance of the HVDC system is studied by simulation under the following conditions: start-up， normal operations， and faulted conditions in the DC links as well as in the AC systems. Simulation results show that the first control scheme is more effective for the hybrid MTDC system， and such system is able to exploit the advantages of both the conventional HVDC system and the VSC-HVDC system. The results also show a new application for the conventional HVDC system.