Single ion anisotropy of Fe3+ ions at each site of the 7 sublattices (2d, 4e 4fⅣ,4fⅥ, 6g, 12k and 4f) in the hexagonal ferrite Zn2-W has been calculated by crystal field theory using point charge model. As expected, the results show that the contributions of diffrent sites are different and may be either positive or negative, thus the experimental results of substituted W-type ferrites can be explained.