Spindle‐type chromophore molecules have been successfully designed and synthesized. Furthermore, a new series of main‐chain second‐order nonlinear PUs with spindle‐type chromophore molecules have been prepared. These PU offered good processability; thus thin films of optical‐quality could be easily prepared from their solutions. The molecular structural characterization of the resulting PU was achieved by 1H NMR and FTIR spectroscopy and elemental analysis. TGA measurement of the PU showed that they had good thermal stability with decomposition temperature higher than 250 °C. The nonlinear electro‐optic coefficient of the PU‐2/poly(MMA‐co‐GMA) doped film was measured up to 32 pm · V−1 by Teng‐Man technique after poling and crosslinking.