Neuronal firing patterns are related to the information processing in neural system. In this paper, we investigate the response characteristics of Chay neuron model to the stimulation of externally-applied sinusoidal electric field. The stimulus frequency is used as the bifurcation parameter. By calculating the inter-spiking intervals (ISIs) and Lyapunov exponents, we find kinds of firing patterns such as period-n bursting, period-n spiking, mixed-periods bursting, bursting-chaos and spiking-chaos. Meanwhile, various phase-locking patterns have been studied in this paper, such as p: 1(p ≥ 2), 1: p(p ≥ 2) and p: q(p, q ≥ 2) phase-locking, etc. Especially, it is easy to control the transition between various firing patterns of excitable cell under external sinusoidal ELF stimulus, which has significance of theoretical guidance for treatment of diseases by the external electric field.