The dynamic balance of excitation and inhibition systems in the cerebral cortex determine the response characteristics of neurons to the stimulation. It has been reported that metformin can induce the postsynaptic clustering of gamma-aminobutyric acid (GABA) receptors and enhance inhibition in the nervous system. Here we explore the regulatory effect of metformin on the balance of the excitatory and the inhibitory system of the primary visual cortex, and its potential to improve visual function in mice. Adult male mice were treated with metformin (metformin group) and normal saline (control group) for 3 weeks of intragastril administration. We found that metformin can significantly increase the production of vesicle GABA transporter (VGAT) and postsynaptic inhibitory receptor-related protein (Gephyrin). Furthermore, it significantly reduced the expression of postsynaptic excitatory receptors GluA1 and GluN1. The data also demonstrated that the multichannel electrode recording shows that Baseline Response and Maximum Response of the primary visual cortex were significantly decreased, while under the treatment of metformin the signal-to-noise ratio, directional and orientation bias were significantly increased. Our finding reveals that metformin could reduce the excitation synapse, enhance the inhibition synapse, and adjust the balance of excitation-inhibition of the primary visual cortex, thus improving information processing ability and enhancing visual function.