The photoluminescence of polyfluorene thin film modulated by an electric field are studied. The results show that the photoluminescence from polyfluorene film can obviously quenched by the extra electric field, which is attributed to the electric field-induced dissociation of photogeneration excitons. The dependence of the exciton dissociation rate constant on the intensity of electric filed is fitted. The average hopping distance of element charge is 0.68 nm in PFO. This volume is comparable with the reported results in Alq3 and polymers. The spectral dependence of the factor of EFIQP is given. The dissociation of hot-exciton is deduced, which influences on the spectral dependence of the EFIQP factor slightly.