TiO2 TiO2 nanotube arrays (NTAs) with different intertube spaces were fabricated via electrochemical anodization process in the electrolyte with different water contents. Uniform distributed cadmium selenide (CdSe) nanoparticles were deposited onto the TiO2 NTAs through electrodeposition method. The influence of water contents in electrolyte on the microstructure and photocatalytic property of CdSe/TiO2 NTAs were studied. The results show that increasing the water content in electrolyte from 2 to 12 vol% can enlarge the intertube space from 0 to 22 nm, which is beneficial for the deposition of CdSe nanoparticles. The photocatalytic activity of CdSe/TiO2 NTAs was evaluated by measuring the degradation of methyl orange solutions under visible light. When water content was 10 vol%, CdSe nanoparticles distributed uniformly on the inner and outer surface of TiO2 NTAs. The photocatalytic tests indicated that CdSe/TiO2 NTAs composites exhibits excellent photocatalytic properties after visible light irradiation for 2 h, the degradation rate reached from 55.7 to 94.5 % when water content increased from 2 to 10 vol%, whereas the degradation rate of the TiO2 NTAs without CdSe modification is just 4.8 %.