Building a new electric power system that is based on new energy sources is an important direction for power system transformation and upgrading in China, and it is critical for peaking carbon emissions and achieving carbon neutrality. In this study, we analyze the changes and challenges that are brought by power system transformation and elaborate on the connotation and building principles of a new electric power system. Moreover, we categorize the development of the new system into stages and propose development suggestions for each stage considering the technical features of the system and the new energy access scale. The new electric power system proposed in this study can satisfy the increasing demand for clean power as it primarily uses new energy sources and it has the features of high safety, openness, and adaptability. Building the new electric power system should follow the technical evolution law and characteristics of power systems; it should further exploit the potentials of mature technologies and current power systems. Meanwhile, emerging technologies should be researched and developed.