The aim of the work is to study the local struture of KCdF

3

doped with Cr

3+

and Li

+

ions by means of the quantitative relationship between the ZFS parameter and the crystal structure.The present work suggests that the tetragonal crystal field of Cr

3+

ion in KCdF

3

:Cr

3+

Li

+

crystals comes from following two origins:(1) The equivalent charge caused by the charge compensation in the [001]-axis direction. (2) The lattice distortions of the nearest-neighbor fluorine coordination.In fact

when Cr

3+

and Li

+

ions doped into KCdF

3

crystals

Cr

3+

ions replace divalent Cd

2+

ions. Owing to the difference in charge

mass

and radius between Cr

3+

and Cd

2+

ion

the lattice distortion occurs to the local structure of Cr

3+

-Li

+

centres in KCdF

3

crystals. Due to the charge compensation

a Cd

2+

ion on [001]-axis will be replace by Li

+

ion. Because of these

the local structure distorts and local point symmetry around Cr

3+

changes from

O

h

to

C

4v

. According to the idea

the relationship between the zero field splitting D and crystal structure for Cr

3+

in KCdF

3

:Cr

3+

Li

+

crystals has been established by means of the superposition model and third order perturbation theory.The EPR zero field splitting parameter

D

has been investigated

taking account of both effect of lattice distortion and the equivalent charge.The calculated result(

D

=-0.06203cm

-1

) is in excellent agreement with experimental result(

D

=-0.06212(5)cm

-1

).Meanwhile

the results

the F

-

ion moves toward the central Cr

3+

ion by

R

1

=0.00268nm

R

21

=0.001nm

R

3

=0.00165nm

are obtained.