A movement of refractive index grating was observed in two-beam coupling behavior with a low glass-transition temperature photorefractive polymeric film as the poling electric field was discharged. The photorefractive polymeric composite is poly(N-vinylcarbazole) doped with 2,5-dimethyl-4-(p-nitrophenylazo)anisole,N-ethylcarbazole and 2,4,7-trinitro-9-fluorenone in a weight ratio of 25:40:34:1. A theoretical explanation based on electrostrictive effect was given, and some evidential experiments, including degenerate four-wave mixing and Michelson interference measurement were also presented. ©1998 American Institute of Physics.