1N-Acetyl-3-(2,4-dichloro-5-fluoro-phenyl)-5-(p-methyl-phenyl)-2-pyrazoline has been synthesized and characterized by elemental analysis, IR, UV-Vis and X-ray single-crystal diffraction. Ab intio calculations have been carried out for the compound by using both B3LYP and HF methods at the 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. The electronic absorption spectra calculated by B3LYP/6-31G* method are approximate to the experiments and the Natural Bond Orbital (NBO) analyses suggest that the above electronic transitions are mainly assigned to n →π* and π→π* transitions. CIS-HF/6-31G* method is not suitable to predict the electronic spectra for the title compound. The calculation of the second order optical nonlinearity was carried out, giving the value of molecular hyperpolarizability equal to 2.194*10-30 esu. On the basis of vibrational analyses, the thermodynamic properties of the compound at different temperature have been calculated, revealing the correlation between C0p, m, S0m , H0m and temperature.