Plasma focus is one type of ion source with energy up to few MeV. While some efforts have been made to understand the physics of ion beam acceleration in plasma focus devices (PFD), an acceptable clarification does not exist yet. In this work, the procedure of ions) electrons) acceleration in PFDs to the MeV energy is investigated theoretically. Moreover, the trajectory of electrons (ions) and their angular distribution are studied. The simulations are carried out by COMSOL Multiphysics version 5.2 for a 4.5 kJ Mather type PFD. The results of simulations and calculations show that trapped ions in the negative potential of electrons, their movement toward the top of the anode and the drift motion due to electrical and magnetic fields near the top of the anode are the main causes of high energy electrons (ions) production and acceleration.