In external electrical field,the self-trapping biexciton in non-degenerate ground state conjugated polymer has an abnormal characteristic-its static polarizability was found to be negative.We calculated the dynamic response function χ(ω) of biexciton.By putting ω to the zero limit,we got the static polarizability χ which proved to be negative.We compared it with that of self-trapping exciton and ground state and gave some analysis on the origin of negative polarizability.Finally,we investigated the behavior of χ(ω) when ω is small,and deduced that if more biexcitons are excited,the n(ω) of the material will decrease,whereas if more excitons are excited,the n(ω) will increase.