The relationship between transmission capacity and voltage level of the voltage source converter（VSC）-HVDC is analyzed. The method for determining the scope of economical transportation is proposed. It emphatically analyzes such economic parameters as the total cost of the VSC-HVDC project， annual operation cost， maintenance cost， and the fund recovery period. A typical VSC-HVDC line is used as an example. The study shows that， by taking into account the factors such as the converter station， cable and environment for a project of a few hundred MW-level VSC-HVDC， the higher the voltage level is， the lower the operation and maintenance cost of the project will be. Furthermore， considering the loans， electricity sales， investment income， internal revenue， etc， the higher the voltage level is， the lower the total investment of project cost， and the shorter the investment recovery period. So the selection of a proper voltage level can improve the economy of the VSC-HVDC project.