A water-soluble palladium complex (PdL_n@β-CD) was designed and prepared based on functionalized β-cyclodextrin. It showed high turnover numbers (TONs) and turnover frequencies (TOFs) of up to 9.9 × 10⁸ and 4.9 × 10⁸ h⁻¹, respectively, in aqueous Suzuki–Miyaura coupling reactions. The detailed reason for the excellent catalytic activity was studied.