With the rapid development of renewable energy generation in China, the difficulty and cost of power system regulation keep rising. In the beginning of 2023, STATE GRID Corporation of China put forward the principle of “Three Balance” of power system, which essentially are “local power balance”,”nearby power balance” and “cross-regional power balance”, to provide a novel perspective for provincial power system operators to economically dispatch the power system and purchase the flexible resources. Aiming at the background of new power system construction and the challenges of high penetration rate of renewable energy generation, this paper put forward day ahead dispatching model of power system considering the principle of”Three Balance”. The cost of risk is introduced into the optimization model to namely arrange the power generation plan and prepare the flexible resources for mitigating the volatility of renewable energy. The case study shows that the proposed model can scientifically coordinate multiple types of power generation resources within and outside the province.