The first hyperpolarizabilities β(-2ω;ω,ω) and β(-ω;ω,0) of hemicyanine derivatives chromophore, 4-N,N-dimethylamino-4'-N'-methyl stilbazolium (DAS), are calculated by using time-dependent Hartree-Fock (TDHF) and sum over states (SOS) method at infrared wavelength, respectively. Frontier molecular orbitals are also computed by INDO/CI method. The numerical results indicate that maximum absorption wavelengh is about 480 nm which agrees well with the experimental data, and nonlinear optical properties are determined by the first excited state. In infrared region (800～2500 nm), with the increase of fundamental frequency, secondary harmonic generation (SHG) β(-2ω;ω,ω) and electrooptic effect (EOE) β(-ω;ω,0) also become larger, but β(-2ω;ω,ω) increased greater than β(-ω;ω,0). In off-infrared region, β(-2ω;ω,ω) dispersion curve is flat while sharp caused by resonance enhancement in near-infrared region (<1300 nm). β(-2ω;ω,ω) equals to (380±5)×10-30 esu at 1064 nm calculated by TDHF. However, for the higher frequency, other excited states should be considered in SOS calculation. Moreover, influence of basis set effect upon TDHF calculation is also discussed.