Abstract: Liquefaction of calcareous sand foundations is a major cause of seismic damage to critical infrastructure, including breakwaters, wharves, and airport runways. Fiber reinforcement, an environmentally friendly geotechnical materials, can effectively improve the liquefaction resistance of calcareous sand and exhibits great promise for island and reef engineering in the South China Sea. In this study, a series of undrained cyclic simple shear tests were conducted to examine the effects of fiber content (F_c) and cyclic stress ratio (CSR) on excess pore pressure, deformation, and liquefaction resistance of fiber-reinforced calcareous sand. A new prediction model for excess pore pressure development of fiber-reinforced calcareous sand was proposed based on the test results. The findings show that increasing F_c significantly reduces the accumulation rates of excess pore pressure and shear strain, thereby enhancing liquefaction resistance, whereas the reinforcement effect weakens as CSR rises. Fiber reinforcement also alters the deformation pattern of calcareous sand during liquefaction and effectively inhibits the occurrence of sharp increase in deformation. Furthermore, the excess pore pressure development in fiber-reinforced calcareous sand differs significantly from that in siliceous sand, and it presents a faster excess pore pressure accumulation rate under the same cyclic ratio, resulting in the traditional Seed model inadequate for accurately capturing its evolution. With increasing CSR, excess pore pressure development pattern shifts from S-shaped to hyperbolic, while higher F_c induces the opposite trend. These results provide important theoretical support for applying fiber reinforcement to liquefaction mitigation in island and reef infrastructures.