In poled electro-optical (E-O) polymer systems, the relaxation of oriented chromophores is maintained by either introducing the guest chromophores into host polymers with high glass transition temperatures, or by confining the chromophores in polymer networks. Various highly stable NLO polymers have been prepared by grafting NLO-active chromophores onto aromatic polyimide backbones. The pendent chromophores of side chain polyimides can be stabilized at low temperature because they have rigid rod-like structures. However, the orientation decays quickly at elevated temperatures because the local free volumes that surround the chromophores increase. Taking advantage of the multifunctional characteristics of carbazole along with rational molecular design, a new NLO-active lambda-shape main-chain polyimide that comprises the two-dimensional carbazole chromophore was synthesized. This polyimide exhibits high thermal and temporal stability. it can endure as high as 240 °C in a transient time and maintain large SH signal at 100 °C for a long time. The high-glass transition polyimide as a matrix and embedding the two-dimensional chromophore into the polymer backbone are the major reasons that effectively restrict randomization of the oriented dipole.