Transcranial alternating current stimulation (tACS), as a non-invasive neuromodulation technique, is widely used in fields such as neuroscience research, making it an important tool for exploring the working mechanisms of the nervous system and understanding brain functions. Based on the Izhikevich neuron model, this paper investigates the response characteristics of excitatory and inhibitory neurons under varying stimulation intensities of alternating current. The results indicate that the stimulation intensity significantly influences neuronal firing behavior: as the stimulation intensity increases, the firing frequency of both types of neurons increases, the half-peak width shortens, and the peak amplitude of action potentials increases after the stimulation intensity reaches a certain level. Meanwhile, the membrane potential amplitude first rises and then declines. These findings reveal that transcranial alternating current stimulation can modulate neuronal excitability by adjusting the stimulation intensity, providing theoretical guidance for the practical application of alternating current stimulation.