H. Kawamura studied the solid-fluid phase transition of a two-dimensional hard disk system by using the Collins' model, but the 4 co-ordination was neglected. In this paper, we have taken into account the 4 co-ordination and the attractive interaction. The thermodynamic functions of the two-dimensional system are calculated. The dependence of the transition point on the percentage of 4 co-ordination is studied. The equation of state and specific heat are discussed.