Given that the construction of step-scheme (S-scheme) system could prolong the lifetime of more reactive charge carriers, a novel S-scheme photocatalyst AgI/BiO(CH3COO)(x)I1-x (denoted as AgI/I-BiOAc) was constructed via a facile and green one-pot milling method. The as-prepared AgI/I-BiOAc S-scheme photocatalyst with the optimized ratio of Ag/Bi at 0.8 exhibited superior visible-light photocatalytic performance for the degradation of methyl violet (MV), methyl orange (MO), malachite green (MG), and colorless bisphenol A (BPA), which was better than AgI, BiOAc, I-BiOAc-0.4, and even AgI/BiOAc heterojunction. Mott-Schottky analysis indicated that the formation of I-BiOAc solid solutions with suitable I content could optimize energy band structure, which transformed type-I AgI/BiOAc heterojunction to typical S-scheme AgI/I-BiOAc photocatalyst. Furthermore, owing to in situ preparation of AgI/I-BiOAc, the as-prepared S-scheme photocatalyst possessed closely contacted interfaces, which is beneficial to the transfer and recombination of electrons and holes with low redox ability, thus maintaining charge carriers with high redox capacity. The S-scheme mechanism was further verified by electron spin resonance (ESR) and the radicals trapping experiments. This work provides a facile way to design S-scheme system by modulating the composition of the solid solutions.