Abstract: Focusing on new power system's power balance mechanism and development, basic rules of power balance are revealed with theoretical analysis, simulations as well as real power system operating statistics. First, basic power balance equations of new power system are proposed, based on which senior power balance equations are deducted. With the analysis and conclusions of the proposed equations, 5 rules of new power system's power balance mechanism are proposed to describe relations among key balancing factors, such as the penetration rate of renewable energy, renewable energy consumption, and the regulation capability of the power system. Then, all the equations and rules proposed are verified by simulations and statistics based on real power system operating data. Finally, the key rule during the development of new power system's power balance is revealed, which is the contradiction between unlimited regulating demand growth of new energy and limited regulating abilities of power system. The New Power System will go through 2 key developing points and 3 key developing stages. Prospects are made for the future development and construction direction of the new power system, and relevant suggestions are put forward.