To address the issues of high cost and complex control associated with traditional two-port thyristor-based solid-state DC circuit breakers when extended to multi-port DC microgrids, a novel multi-port solid-state DC circuit breaker is proposed. The key idea is to employ an LC resonant circuit to achieve active and reliable turn-off of the thyristors in the conducting branch. By using a discharge circuit formed by the internal capacitors and the circuit, the proposed breaker identifies fault characteristics through the peak value of the discharge current, thereby enabling adaptive reclosing. Furthermore, the LC resonance is exploited to rapidly restore the capacitor polarity to its initial state before reclosing, eliminating the need for additional capacitor charging time. An equivalent mathematical model of the proposed topology for an n-port DC grid is established, and design principles for the key component parameters are presented. Both simulation and experimental results demonstrate that the proposed circuit breaker can achieve rapid fault interruption and adaptive reclosing. Compared with existing solutions, it offers superior economic efficiency and operational performance, providing a practical protection solution for multi-port DC microgrids.