Vigorously developing new energy sources is an important approach to achieving the carbon peaking and carbon neutrality goals. However, the randomness, volatility, and intermittency of new energy pose severe challenges to the supply-demand balance and stability of the electric power system. Therefore, there is an urgent need to develop diversified flexible resources to guarantee the system’s safe and stable operation. This study summarizes the electricity demand and the power structure development pathways in China under the carbon neutrality goal. Based on this, it analyzes the different flexibility demands of electric power systems with different proportions of wind and solar power generation capacities and elaborates on the characteristics of various types of flexible resources needed for power generation, transmission, load, and storage from four aspects: peak capacity (adequacy), ramping flexibility, stability, and inertia. Drawing from the international experience regarding flexible resource development, we propose the principles for flexible resource development: supply security guarantee, low-carbon development, and economic optimization. Considering the existing problems in the flexible resource development in China, we propose a flexible resource development pathway that aligns with the emission reduction goal of the power sector and the medium- to long-term development trend of the electric power structure of China. Furthermore, key initiatives to ensure the development of flexible resources are proposed from five aspects: power source, power grid, load, energy storage, and market mechanism.