This paper presents a new model of optical bistability (OB). In view of the ideas of the mean field approximation, the slow envelope approximation and the adiabatic approximation, the OB system can be regarded as a "box". Comparing with the theory of nonlinear oscillation, we find that the courses in different OBS s-includingdifferent substances and different cavities (E-P. C. or E. C. )-can be describedconsistently, in both steady state and temporal respect, with an appropriate nonlinear forced oscillation theory, we develop the equation iniio a coupling and autonomous dynamic equation set of phase and amplitude. The general solutions of the equation set for OB eteady state and transienii beliavior are obtained conveniently from this form. Several concrete results in literaiiure are compared as the examples for the veriiication of the widely applicability of this model.