Abstract: Existing old masonry structures are a vulnerable bottleneck in the earthquake prevention and in the disaster reduction in China, which has become a research focus in the field of seismic strengthening for existing buildings. In response to the significant disturbance and performance defects of traditional strengthening techniques, a strengthening layer based on basalt fiber reinforced cementitious composites (BFRCC) was proposed and applied to strengthen unreinforced masonry walls. The strengthening effect of the BFRCC layer was investigated and verified by diagonal shearing tests. A separated finite element model was established and validated, and a parametric analysis was conducted to reveal the influence of different effectors on the shearing strengthening efficiency. BFRCC can significantly enhance the in-plane shearing resistance of unreinforced masonry wall by 2.38~5.15 times. Both the thickness of the BFRCC layer and the strength of masonry mortar have significant impact on the strengthening effect while the brick strength has little effect.