To quantify single DC and DC group carrying capacity and improve the absorption capacity of clean energy in a hydropower sending power grid, this paper puts forward a method to evaluate and improve the DC carrying capacity. First, the characteristics of DC carrying capacity affected by power flow organization, frequency stability, voltage stability and ultra-low frequency oscillation are analyzed. A calculation method for DC carrying capacity with security constraints is proposed. Operational risks of the grid under different operating conditions and faults are quantified, and an optimization model of planning measures is established. Finally, the planning and operation of a power system are coordinated through the search for maximum investment benefit measures. Simulation results on a practical power system show the method can provide a reference for measure selection and distribution, and improve DC carrying capacity to the greatest extent. This work is supported by the National Key Research and Development Program of China (No. 2017YFB0902000) and the Science and Technology Project of State Grid Southwest Branch “Analysis and Improvement Strategy Research of DC Carrying Capacity in Large-Scale Hydropower Sending Power Grid”.