An external electric field (EEF) has a strong controlling effect on the structure, electron distribution, and optoelectronic properties of a system. In this study, the geometric structure, electronic distribution and electronic transition properties of [6,6] carbon nanobelt ([6,6]CNB) were investigated under different EEFs based on density functional theory and wave function analysis. These theoretical studies determined that EEF can significantly change the geometry of [6,6]CNB by elongating its structure. The system deformation was mainly caused by forces pulling in the direction of the EEF. After removal of the EEF, the system reverted to its original structure. Electronic polarization played a major role in structural stability during the deformation process. The changes in geometric structure and electronic distribution affected the photoelectric properties of [6,6]CNB. Under the action of EEFs, the absorption peak of [6,6]CNB was red-shifted and gradually appeared in the visible light region. This study facilitates an understanding of the performance of [6,6]CNB as a new type of nanomaterial and provides the necessary theoretical basis for the application of [6,6]CNB in the field of optoelectronics.