Mixed hammered ash, with both hydraulic and air hardening properties, was used in restoring Leshan Giant Buddha. To solve the problems of cracking and peeling in the Buddha’s head and face caused by environmental factors, hemp fiber (HF) and calcium carbonate whisker fiber (CWF) were added to enhance the material. Results show that HF outperforms CWF in improving flexural strength, while adding CWF effectively enhances toughness and tensile strength. The combination of the two achieves a comprehensive strengthening effect. After 28 days of curing, composite specimens show a 35.73% increase in flexural strength and 20.88% in tensile strength, outperforming single-doped groups and showing better water and acid resistance. This multi-scale fiber composite method achieves a comprehensive improvement in material strength and weather resistance.