Abstract： A theoretical study of the properties of the ground state and excited state of FH(CN)- de-fect pair in KC1 crystal has been conducted by using the SLC extended-ion method. The resul-ts of the calculation for electronic absorption and emission are in good agreement with the ex-periments. Under the harmonic approximation, we calculate the frequencies of the (CN)- stretching vibration. It is reasonable to attribute the observed splitting into four components in Ra-man vibrational spectrum to the four inequivalent (CN)- orientations with respect to the  neighboring F centre. Finally, the e-v energy transfer processes has been studied, It is pointed out that during the relaxation process polarization causeed by the change in F electrcr nic state would excite the (CN)- stretching mode from m = 0 to m = l.