Abstract: The standardized DC voltage level sequence and the economical effective selection methodology for DC voltage level of newly proposed DC transmission systems can provide the basis and tools for the DC transmission project planning. Considering that DC grids will be gradually developed by the newly proposed DC transmission systems as a precondition, how to select and determine the DC voltage level based on the standardized DC voltage sequence is a problem to be solved. This paper analyzed the influencing factors of DC voltage level selection of DC grids including transmission distance, rated current, capital costs, operational costs and interconnection equipment costs. The DC voltage level selection methodology for DC grids was proposed by considering various technical and economic factors including current limit, operational losses and equipment costs on the premise of defined DC transmission capacity and distance. According to whether there is a DC transmission system/grid nearby the newly proposed DC transmission system, five different examples of three scenarios were considered and analyzed as case studies for a newly proposed DC transmission system to determine its DC voltage level based on the proposed selection methodology. The optimal DC voltage levels for the five scenarios were obtained. At the same time the voltage ratio of a DC/DC converter was also obtained if it is required to interconnect the newly proposed system with the existing DC system/grid at different voltage levels.