In order to study the physical properties of potassium fluoride，the bond length，energy，charge dis- tribution，energy level distribution，energy gap and infrared spectra of KF molecules under different applied electric fields ( -0.02 ～ 0.02 a.u.) are investigated by density functional theory LSDA method at the level of 6-311G radical group. The results display that the applied electric field has a great influence on the structure of KF molecules. With the increase of the external electric field in the direction of Z ( F-K bond) ，the bond length and electric dipole mo- ment of KF molecules have been decreased，the total energy has been increasing，and the energy gap EG has been increased first and then decreased. At the same time，the strongest peak of the KF infrared spectrum undergoes a blue shift; The first 10 excited states are

redshifted. On the other hand，as the electric field strength increases，the dissociation energy of KF molecules increases，and vice versa，the dissociation energy decreases.