It is a multi-objective and multi-constraint, non-linear optimization problem that the maintenance scheduling of transmission equipment in interconnected large power grid needs to consider the guarantee of renewable energy transmission capability and the operational safety of regional power grids. Therefore, a method of maintenance scheduling of transmission equipment based on improved gravitational search algorithm (GSA) is proposed: one of the optimization objectives is to calculate the electric quantity of the abandoned renewable energy. In addition, considering the safety constraints of the operation of the interconnected power grid, the optimization model of the maintenance scheduling is established, and GSA method is used to solve the model. By introducing the idea of simulated annealing (SA) and using the Metropolis criterion to update the particle position according to the probability, the particle degradation in the GSA is reduced, and then the overall convergence and accuracy of the algorithm are improved. The annual maintenance scheduling of the actual power grid is verified as a calculating example.