Currently, the extended Hubbard model, which is a good approximation only for narrow-band system, suggests that the width of polaron in polymer is heavily reduced by the electron-electron interaction. However, the polymers possess wide band, so the off-diagonal correlation cannot be neglected. We considered the effects of full electron-electron correlation on the width and the creation energy of polaron in polymer. In the case of strong screening, our results are greatly different from those of Hubbard model. This suggests that in polymer, the Hubbard model should be gone beyond.