The study on the harmonic characteristics of HVDC transmission system is important for analyzing the effect of harmonics on the operation of the electrical installation and the system. The new HVDC transmission system adopts the new converter transformer and the corresponding inductive filtering method, and it is a new electrical topological structure. As for a new system, the harmonic characteristics of the new HVDC transmission system are completely different from that of the traditional one. This paper introduces the main circuit topology of the new HVDC transmission system, and then analyzes the connection of the new converter transformer and the filtering mechanism of the inductive filtering method. Based on these, the mathematic model has been established to calculate the harmonic characteristics of the new HVDC transmission system. Furthermore, the amplitude and phase angle of the main characteristic harmonics of the new HVDC transmission system have been calculated by the established mathematic model and then simulated by MATLAB/SIMULINK Tested results have verified the correctness of above analysis and calculated results. The research findings are useful for the design of the characteristic parameters of the new HVDC transmission system, the selection of the wire cross-section of the new converter transformer, and the design of the inductive filtering installations.