Three series of BiOM(x)R(1-x) (M, R = Cl, Br, I) solid solutions were systematically synthesized through a low-temperature precipitation. These solid solutions were characterized by XRD, FESEM, TEM, EDS, UV-vis spectra, nitrogen sorption/desorption, and PL. The tunable band gaps of the as-prepared solid solutions were realized via only changing the molar ratio of two halide ions. Meanwhile, the influence of citric acid in the formations of controllable morphological structures was discussed to study the growth mechanism of solid solutions. The photocatalytic activities of the bismuth oxyhalide solid solutions have also been investigated by the degradation of Rhodamine-B (RhB) under visible light irradiation. The optimized solid solutions possess higher photocatalytic activity than pure ones [BiOM (M = Cl, Br, I)] due to the broadened range of visible light response and the reduced recombination rate of electron-holes pairs. The results show that the synthesis of BiOM(x)R(1-x) (M, R = Cl, Br, I) solid solutions have profound significance for the design of the novel photocatalyst materials.