Picosecond time-resolved two-wave coupling method is used to investigate the excited-state enhancement of the third-order nonlinear optical process of a organic polymer──non-ether PPQ (polyphenylquinoxalines). The enhancement factor of the material's effective third-order hyperpolarizability γ is observed to be 2 under the nonsaturable exciting condition, and excited fluorescence of non-ether PPQ was also examined. We verified that the excited-state enhancement of γ is proportional to the population of the population of the excited state, and explained the time process of the enhancement using three-level model.