Abstract：Under the dual carbon background of AC and DC hybrid power grids have the new feature of

"strong HVDC and weak AC system" and power electronization，in order to effectively reduce the risk of largescale

power outages in power grid，it is necessary to build a secure and reliable comprehensive defense system to

ensure the stable operation of the power system. Based on the traditional three defense lines in China，the objectives and design principles of the UHV AC and DC power grid security defense system that adapt to the dual carbon background of China's power grid were determined，and designed the overall structure of the UHV AC/DC power grid security defense system，main functions and specific configuration schemes.

      Key words：hybrid power grids；comprehensive defense system；three defense lines；configuration schemes