A new strategy for postfunctionalization performed on poly(N-vinylcarbazole) (PVK) has been explored to develop PVK-based nonlinear optical (NLO) polymers with a high density of chromophores and improved comprehensive properties. Thus, under the standard Vilsmeier reaction conditions, PVK is partially formylated to a high degree (up to 52% molar ratio), and these formyl groups of high reactivity are condensed with cyanoacetylated DR-1 to afford a DR-1 functionalized PVK in almost complete conversion. The Tg of the resulting polymer is 185℃, and the orientation behavior of its poled film is studied by UV-visible spectroscopy. The NLO activity, which is estimated to be 20pm/V by in situ second harmonic generation measurement, remains unchanged at 120℃ for over 1000h after a minor initial drop.