Flexible low frequency AC transmission technology combines the advantages of both conventional AC power frequency and DC transmission, offering significant potential for application in medium-to-long distance offshore wind power connection. However, in such scenarios, wind power is transmitted through long-distance submarine cables. In the event of a cable fault, the fault current characteristics are influenced by the controlled power sources at both ends, leading to a decline in the performance of current differential protection. Additionally, the long low-frequency period, coupled with the effect of the distributed capacitance of the long submarine cable, results in slow fault discrimination for the protection system. This can cause wind turbines to disconnect from the grid, threatening grid security and stability. To address this, a pilot protection scheme for submarine cables in offshore wind power flexible low frequency transmission systems is proposed based on dynamic state estimation. A submarine cable model is established considering the structure of each metallic layer of a three-core submarine cable and its distributed capacitance. By utilizing the redundancy characteristics of dynamic state estimation of instantaneous values, the speed and reliability of the proposed protection method are improved. A protection criterion is constructed based on the matching degree between the developed cable model and the physical cable. Simulation results show that the proposed protection method can reliably discriminate various internal and external faults within 5 ms and exhibits strong tolerance to transition resistance and interference.