Visible-light-driven photocatalyst BiVO₄ was synthesized via a facile microwave-hydrothermal method using BiVO₃·5H₂O and NH₄VO₃ as raw materials. Crystal structure of BiVO₄ photocatalyst could be selectively controlled to be tetragonal or monoclinic by simply adjusting the pH of the precursor solution. The prepared samples were characterized by XRD, UV-Vis, Raman, and SEM. The mechanism of BiVO₄ formation with different crystal structures was discussed. Meanwhile, the photocatalytic performances of the prepared sample were evaluated by degradation of methylene blue and photocalytic oxidation of NO gas in air under visible light irradiation. The results showed that BiVO₄(z-t) microsphere was obtained when the precursor pH is 3-5, but when the pH is less than 2 or greater than 7, the as-prepared powders are BiVO₄(s-m) with polyhedron morphology. This may be due to the change of pH that could form transformation of vanadate and bismuth ion in the precursor solution, and then affect the formation process of BiVO₄, resuting in the change of crystal structure, morphology, crystal surface, and VO₄ tetrahedron of BiVO₄(s-m). The photocatalytic tests indicated that the activity of BiVO₄(s-m) was much better than that of BiVO₄(z-t). The BiVO₄(s-m) sample prepared at pH 9 exhibits excellent visible-light photocatalytic activity, because of its higher crystalline, preferentially exposed facts (040), and higher degree distortion of VO₄^3- tetrahedron.