The Mad2 protein, with two distinct conformations of open-and closed-states, is a key player in the spindle checkpoint. The closed Mad2 state is more active than the open one. We carried out conventional and targeted molecular dynamics simulations for the two stable Mad2 states and their conformational transition to address the dynamical transition mechanism from the open to the closed state. The intermediate structure in the transition process shows exposure of the beta 6 strand and an increase of space around the binding sites of beta 6 strand due to the unfolding of the beta 7/8 sheet and movement of the beta 6/4/5 sheet close to the alpha C helix. Therefore, Mad2 binding to the Cdc20 protein in the spindle checkpoint is made possible. The interconversion between these two states might facilitate the functional activity of the Mad2 protein. Motion correlation analysis revealed the allosteric network between the beta 1 strand and beta 7/8 sheet via communication of the beta 5-alpha C loop and the beta 6/4/5 sheet in this transition process.