It is demonstrated that the mean field (Landau) theory of critical phenomena (including the two kinds of critical point) and transitions can also be applied to the increasing absorption optical bistubility (IAOB), far from equilibrium. On the basis of analysing the dynamical fea Lures of the IAOB model proposed recently[９］, the socalled quasi-thermodynamic potential is introduced. This potential, near the critical point (of the second kind), reflects not only the general properties of phase transitions in bistable systems, but also the specific characteristics of the IAOB.