Abstract: In order to solve the problem of new energy curtailment in the power system with large-scale wind and solar grid-connected power in Northwest China, a source-grid-load multi-time interval coordinated optimization method considering wind-photovoltaic-photothermal combined DC transmission was proposed. Firstly, the peak modulation capabilities of the three sides of the source, grid and load and their complementary characteristics were analyzed. The rapid peak modulation capabilities of the source-side concentrating solar power plants, the grid-side HVDC tie-line and the demand-side flexible load were used to improve wind and solar resources utilization rate. Secondly, in view of the gradual improvement of new energy output and load forecast accuracy in different dispatching stages, considering the different response speed characteristics of various peak modulation resources on the three sides of the source, grid and load, with the lowest comprehensive operating cost of the system was the objective, and a two-stage multi-time interval optimal dispatching method for source-grid-load was constructed. Finally, a simulation example of a power grid 2025 planning structure in a northwest province proved that the dispatching method can effectively improve the level of wind and solar consumption, and reduce the overall operating cost of the system.