The WO3 was synthesized by the hydrothermal method using sodium tungstate and ammonium tungstate as raw materials, nitric acid as acid source, and malic acid as surfactant. The samples were characterized analysis by XRD, SEM, and Raman. The experimental results indicated that the addition of malic acid was efficient for the synthesis of monoclinic WO3. A high hydrothermal temperature and a long hy-drothermal time were favorable for the formation of monoclinic WO3. The formation mechanism of monoclinic WO3 in the malic acid-assisted hydrothermal process was also given and discussed. Further-more, we investigated the activity of the synthesized tungsten trioxides composite with CuCrO2 in the photocatalytic water splitting. The reaction results indicated that the activity of WO3 was affected by the type of tungsten source, the amount of added malic acid, the hydrothermal temperature, and the hydrothermal time. A preheat-treatment of WO3 before mixing with CuCrO2 was found to significantly promote the photocatalytic activity of the WO3-CuCrO2 compound. The characterization results suggested that the crystallinity of WO3 was improved by the heat-treatment. In this paper, The WO3 composited with CuCrO2 have the activity of photocatalytic decomposition of pure water for produce hydrogen, and more than 8 μmol H2 was produced under the irradiation of a 300 W xenon lamp for 1 h. It is higher than the activity of the catalyst prepared in the early stage of the research group.