Abstract: With the promotion of power electronics, direct current (DC) zone distribution system is to be applied in drilling device of offshore platform, and relay protection is one of the key technologies for the distribution system. The structure features and protection difficulties of the DC zone distribution system is analyzed. With the application of power electronic building block (PEBB) technology, a DC zone distribution system and its relay protection system are set up by replacing the traditional converter and circuit breaker with turnoff converter and capacitor DC circuit breaker. On this basis, fault detection and location, fault current interrupt and fault device isolation are discussed and analyzed. Finally, the method of setting the threshold for protection and the collaborative protection for different protection areas are investigated.