The $\beta$ to $\alpha$ phase transition in Silver Iodide is studied with the (N,V,E) and (N,P,T) molecular dynamics method. In experiments, the phase transition temperature is 420K. Upon heating of beta form, the iodine ions undergo a hcp to bcc transformation and silver ions become mobile. MD simulations for the beta and alpha phase are carried out at several temperatures and the radial distribution functions (rdf) are obtained at those temperatures in the (N,V,E) ensemble. But the phase transition is not found in our calculations. Next the phase transition is studied with the (N,P,T) MD and we find some evidences of phase transition. At 3 Kbars and 2 Kbars the phase transition temperature is 300K. For 3.55 Kbars, the phase transition is lower (200K) than the low pressure case. The phase transition temperature is weakly dependent on pressure in our calculations.