The developed molecular dynamics shows that upon photoexcitation of a conjugated polymer nanofiber, such as poly(phenylene vinylene)s or the polyfluorene family, singlet excitons initially are formed. Through continuous optical pumping, the electron populations of the excitons are reversed. Different from inorganic materials, the electron population reversion not only generates new localized electron states but also destroys the periodic structure of the polymer chain, inducing localized lattice distortion. These localized modes provide one of the channels to form localized lasing emission in a single conjugated nanofiber laser, which is consistent with recent experimental observations.