Abstract: Based on the application and development requirements of power grid, the key technologies of the primary systems of the VSC-HVDC project for the second transmission channel are researched. The key technologies include electricity transmission mode, location of the sending and receiving substation, project capacity, DC voltage level, AC voltage level of the integration grid, project construction scheme, ground scheme, the parameters of the transformer (including capacity, transformation ratio, winding connection,short-circuit impedance,etc.), P-Q operation zone, the AC short-circuit current, the main electrical scheme, etc. The work in this paper has important referencing value for research and project application of VSC-HVDC projects.