Zinc stannate was prepared with ionic liquid-assisted hydrothermal method. The effect of pH value, hydrothermal time and temperature on the crystal structure, morphology and photocatalytic activity had been investigated in detail. The crystal structure, degree of crystallinity and phase purity of the zinc stannate were characterized with X-ray diffractions (XRD). Transmission electron microscopy (TEM) is used to analyze the morphology of the prepared zinc stannate. The photocatalytic activity of the samples was evaluated using degradation of methylene blue under ultraviolet light irradiation. The results indicated that the Zn2SnO4 sample prepared at pH 9, 220 ℃ and 32 h showed the highest activity for photocatalytic degradation of methylene blue. Research on the photocatalytic mechanism of degradation of methylene blue with Zn2SnO4 suggested that the difference in photocatalytic activities of the samples was mainly attributed to defects which can act as recombination centers for photoinduced electrons and holes, reducing the total photocatalytic activity; OH· radicals were the dominant photooxidants.