Gallium nitride (GaN) nanobelt with a quasi-one-dimensional structure possesses good piezoelectric and photoelectric properties. In this paper, the electromechanical coupling properties of single GaN nanobelt under optical modulation are studied by conductive atomic force microscope. The GaN nanobelts with good crystallization are prepared by the chemical vapor deposition method, then they are ultrasonically dispersed on a highly oriented pyrolysis graphite substrate. The conductive probe is used as a microelectrode to construct the two-terminal piezoelectric device based on a single GaN nanobelt, which has good electromechanical coupling performance. By changing the loading force of the probe and introducing an external light source to regulate the current transport properties of GaN nanobelt, the coupling between mechanical and semiconducting properties under light modulating is studied. It is found that the coupling between mechanical and semiconducting performance of the single GaN nanobelt can be effectively modulated by an external light source, and the electromechanical switch ratio of the single GaN nanobelt increases obviously in the presence of light. With the loading force increasing, the current response of the single GaN nanobelt increases but the rectification characteristics decrease. Finally, the experimental results are explained by the piezoelectric electronics and photoconductivity theory. This work is expected to provide a scientific basis for the performance modulation of nano-piezoelectric optoelectronic devices based on low-dimensional GaN nanomaterials.