This paper presents some new study results on the threshold conditions and characteristics of lasing output for an organic polymer optical multi-stable system in which the medium is with pumping and the system acted with inject signal. The dynamics of light field in the medium are described with the extended forced oscillation model of optical multi-stable and lasing system. Moreover, through the theoretical analysis and numerical analogue, the gain threshold condition of amplifying under population reversion is discussed. Meanwhile the characteristics of the lasing output state with inject signal inspected. Further, the relationships of the amplifying multiple of the incident light field with the cavity detuning; and that with the two-photon detuning; also that between the two kinds detuning are found by analyzing the stationary equations. Finally, theoretical and numerical analyzing shows that the lasing frequency characteristic of such an organic polymer system with pumping and inject signal is different from the common laser. These results should be significant in some degree for both theoretical and experimental research, also application purpose.