Large-scale centralized integration of renewable energy and clustering power transmission is one of the important characteristics of sending-end power system in China. Given this feature, the day-ahead optimal scheduling problem of a regional sending-end power system with large-scale renewable energy integration is studied. The system is composed of several relatively independent subsystems. Based on the analytical target cascading method, a two-level optimal scheduling model for the regional sending-end power system is constructed. The upper-level scheduling solves the coordinated optimization problem for the tie-line active power flow of each independent subsystem; the lower-level scheduling is the relatively independent day-ahead optimal dispatching for each subsystem. From the characteristics of each subsystem, the minimum operating cost and the minimum deviation of the power transmission are the optimization objective functions, and the constraints of DC clustering transmission and wheeling are comprehensively considered in the lower-level scheduling. Through the analysis of an example, the effectiveness of the method is verified. This work is supported by the Major Special Projects of Industrial Innovation in Jilin Province (No. 2018C034-7) and the Science and Technology Project of State Grid Corporation of China (No. 522300190009).