Abstract: Positron lifetime technique is one of a few methods sensitive to voids on the mono-atomic scale. The photocatalytic activity of BiVO4 was studied when the degradation of 2,4-dinitrophenol was used as a probe reaction. The effect of calcination temperature on the photocatalytic activity of BiVO4 was analyzed by positron annihilation spectrum. The results showed that the amount of surface defects and the microstructure of photocatalyst changed with the calcination temperature. More surface defects，amount of photo produced electrons-hole，heterogeneity and the electronic density of defect sites were found on BiVO4 calcined at 900 ℃ than other temperatures，which increased the photocatalytic oxidation activity of BiVO4，that is，the degradation rate of 2,4-dinitrophenol was increased.