An azo-carbazole dye has been known to show efficient dynamic holography characteristics. In order to investigate its mechanism, we made simultaneous measurements of two-beam coupling (TBC) in situ and four-wave mixing (FWM) for the azo-carbazole dye, 3-[(4-Nitrophenyl)azo]-9H- carbazole-9-ethanol (NACzEtOH) doped in a polymer. The results showed fast temporal response with excitation at 532nm, and slower rise and decay processes monitored at 785nm. On the other hand, when excited at 633nm only slow responses were observed. Simple analysis suggests that fast process was originated from photo-induced reorientation of the azo-carbazole dye and slower process was mainly caused by the following alignment of polymer matrix which played an important role for image preservation.