The direct counting method of the chain configurations has been proposedfor calculating the thermodynamic quantities of a single self-avoiding walk chainwith the neighbour interaction on a simple cubic lattice The configurational entropy of the chain lengths 10～18

the energy and the average number of contact betweennonconnective segments VS．the energy of one contact ∧ε have been calculated．It isshown from the results that the maximum of the configurational entropy of the chainoccurs at the athermal case．In the good solution the chain coil becomes loose and the entropy tends to a finite value；in the poor solution the chain coil becomes verydense and the entropy decreases drastically．