Abstract: Low-frequency transmission technology has enormous potential for application in the field of medium-and long-distance offshore wind power. Current differential protection is a widely used traditional AC protection, and its performance may be impacted when facing power electronic power sources. Therefore, it is necessary to study its adaptability in offshore wind power low-frequency transmission systems. The paper derives the influence of source characteristics of permanent magnet synchronous generators and modular multilevel matrix converters on fault current based on fault composite sequence networks, and theoretically analyzes the adaptability of current differential protection. To quantitatively analyze the adaptability of protection, a fault electrical quantity calculation method based on improved node equation is proposed, which calculates the fault current and protection criterion values under given fault conditions, and judges the protection operation situation. Research shows that the sensitivity of protection decreases and may even fail to operate during single-phase-to-ground and two-phase short-circuit faults. The protection can operate normally under two-phase-to-ground and three-phase short-circuit faults. Finally, a PSCAD/EMTDC simulation model is established to verify the correctness of the theoretical analysis and calculation methods.