Photofabrication of surface relief grating (SRG) on azobenzene functionalized polymers was investigated in order to elucidate the dynamics of this phenomenon. The systematic study examined the influence of experimental and geometrical parameters such as the film thickness, the irradiating light intensity and the spacing of the interference light pattern. Experimental results were discussed within the framework of existing fluid mechanics model. The cubic dependence of SRG inscription rate on the film thickness (h) in the small h region and an asymptotic tendency in the large h region were well characterized by the model. We established that the writing behavior of photofabricated SRG depends on the irradiated light intensity. The effective critical intensity of the irradiating light was found to be independent of the spacing of the interference light pattern. it was discussed in terms of the viscosity change of the polymer film caused by light irradiation and viscous fluid nature of the system during the SRG photofabrication was suggested.