Transient grating of biphotonic holography is studied theoretically and experimentally in trans-cis isomerization azo materials. The theoretical description of the transient biphotonic holographic grating agrees well with experimental results in methyl yellow-polymethylmethacrylate and ethyl orange-polyvinylalcohol films. The mechanism of the biphotonic holographic grating in the azo materials can be attributed to the redistribution of cis isomers induced by both the short-wavelength light and the long-wavelength light, which is confirmed by the experimental results of polarized biphotonic holography.