Under the “dual carbon” goal, China’s installed capacity of renewable energy is rapidly increasing, and a pattern of multi DC power grids with high proportion of renewable energy is gradually forming. Under the combined control of renewable energy and DC system, the controlled characteristics of power electronics become more prominent, and the fault characteristics of transmission lines undergo significant changes. Consequently, the adaptability of traditional protection principles are facing severe challenges. This paper studies the typical controlled fault characteristics of line faults in multi DC power grid with high proportion of renewable energy, clarifies the adaptability issue of reduced sensitivity in traditional current differential protection, and proposes an improved double-K current differential protection. Simulation results verify the adaptability issue of current differential protection and the reliability of the improved double-K current differential protection.