The 2D BiOCl nanosheets with excellent photocatalytic activity were synthesized via the facile hydrothermal method by regulating the pH value of the precursor solution and using dulcitol (C6H14O6) as the surfactant. The photocatalysts were characterized by XRD, FT-IR, SEM, TEM, BET, XPS, ESR, O-2-TPD, EIS, DRS and PL. The results of morphological and structural characterization indicate that the pH has a large effect on the thickness of the nanosheets and the exposure ratio of {0 0 1} facets. The photocatalytic property of the sample prepared at pH 4 showed excellent visible-light photocatalytic performance to degrade RhB owing to the small thickness, the exposed {0 0 1} facets and the optimum concentration of oxygen vacancy. Moreover, the reasonable photocatalytic mechanism was revealed by the active species trapping experiments and ESR characterization, which suggested O-center dot(2)- and h(+) are the main active species in the present system.