The effect of electric field on the luminescence and exciton in polymer is studied in two aspects: 1. In strong electric field, the exciton is dissociated into a pair of positive and negative polarons. This dissociation can quantitatively indicate the electric-field-induced luminescence quenching in electroluminescent polymer m-LPPP observed recently. 2. The π　electrons in polymer possess delocalization, they are easily polarized. It is shown that the exciton in polymer has huge polarizability, which is 103 times larger than that of hydrogen atoms.