The self-trapped exciton in polymers under the electric field has been studied using a tight-binding model including the electric field, symmetry-breaking term te and electron-lattice interaction simultaneously. It is discovered that the electric field will polarize the self-trapped exciton in polymers. The polarization depends on the electric field E and te. When te≤0.1eV，self-trapped biexciton in polymers shows the characteristic of the reverse polarization, i.e., electrons move along the direction of E; however, plus charges move along the minus direction of E. The cause of the polarization has been discussed.