The behaviour of defect particles in a two-dimensional (2D) confined dusty plasma system is investigated by molecular dynamics (MD) simulations. The mean square displacement (MSD) and the pair correlation function g(r) are used to characterize the structural and dynamical properties of the system. The influences of the number and the charge (mass) of the defect particles on the system configurations are simulated. All the defect particles with charges (masses) larger than the normal particles have the trend to move towards the system centre. The moving speed of the defect particles towards the centre increases with the increasing number and charge (mass) of defect particles and with the system temperature.