The N=N bridge in azobenzenes molecules with push-pull structures at the two ends provides excellent channels for electrons. This is an advantage for generation of nonlinear optics effect. And the nonlinear optical properties of the azobenzene compounds are greatly affected by the push-pull electronic groups. The spectra and nonlinear optical properties of Langmuir-Blodgett (LB) films of two kinds of push-pull azobenzene compounds were investigated by using ultraviolet (UV)-visible absorption spectra and second harmonic generation (SHG) technique. The steady mono-molecular film could be formed at the interface of air/water and transferred well onto solid substrates, forming high-quality LB multilayer films for the 4-(nitro)-4′-(amido)-azobenzene (NAA) and 4-(carboxylic)-4′-(amidogen)-azobenzene(CAA) molecules. Because the －NO2 has a stronger ability on pulling electron than －COOH, the transfer of the intra-molecular electron is easier and could form bigger molecular dipole for NAA than that for CAA. So it could have a more significant second-order nonlinear hyperpolarizability. The second-order nonlinear optical coefficient d33 of experimental measurement for NAA and CAA in LB films were 40.8 pm/V and 24.2 pm/V, and the hyperpolarizabilities β were 1.97×10-29 esu and 1.17×10-29 esu respectively. The hyperpolarizabilities β of NAA molecule was about 1.7 times bigger than CAA molecule′s. The experimental results agreed well with the theoretical calculation.