A multi - provincial complementary operation index under the province-based scheduling model is proposed. Firstly, the operating status and power exchange needs of each province is claculated under independent operating conditions, and then the complementarity of the inter -provincial grids is calculted through the complementarity of the power exchange curve, which not only ensures the independence of each provinces, but also ensures the mutual benefit of each province. The solution method is greatly simplified, the physical meaning is clear, and the operation is simple. The simulation example of Qinghai practical power grid verifies the effectiveness of the proposed method. The problem of coordinated operation of Qinghai and surrounding provinces is decomposed into two sub-problems: long-term power purchase and short-term load peak -sharing，using 8 760 hour production simulation. In satisfying the sub-problem of long-term electricity purchase demand in Qinghai, Xinjiang province with excess thermal power is used to solved the problem of seasonal shortage of electricity in Qinghai, which is determined through long -term trading. For the temporary power surplus or shortage, it is solved by mutual aid in Shaanxi province.