Fluorine is the most abundant halogen in the Earth’s mantle. High-pressure and high-temperature experiments show that bridgmanite, the major minerals in lower mantle, can incorporate significate amount of F, indicating that lower mantle may be a potential reservoir for F. Subduction zones are supposed to deliver F and H to deep Earth. Superhydrous phase B, an important hydrous magnesium silicate in subduction zones, plays a key role in the transportation of H from upper mantle to lower mantle, while it may be also a potential carrier of F, since the similar radius between F- and OH-. Here, we investigated the influence of F on the compressibility of superhydrous phase B, and we found that the presence of F can largely enhance the compressibility of superhydrous phase B. We further propose that the accumulation and decomposition of F-bearing Shy-B is hard to explain velocity anomaly and melting at the uppermost lower mantle.