Lattice dynamics calculations have been performed for beta-9,10-dichloroanthracene and 9,10-dibromoanthracene under pressure. The potential has been fitted to the ambient pressure crystallographic structure and to lattice phonon frequencies of both compounds. The pressure dependence of the structures and frequencies has been calculated. A pressure induced phase transition which resembles the experimental transition is predicted for the chloro derivative at approximate to 3 GPa.