Abstract: The phenomenon of coherence resonance of a nonlinear integral-and-fire model subject to a voltage-gated channel noise and a synaptic noise is investigated. Based on the adiabatic approximation theory, we obtain the approximate expressions of the firing rate (FR), the probability distribution of the first fire (FPD), and the coefficient of variation (CV) of interspike interval of firing. It is shown that the FPD and the FR are non-monotonic functions of the strength of the voltage-gated channel noise and the synaptic noise. Furthermore, by choosing appropriate noise parameter, spontaneous fire of neuron can occur, i.e., the phenomenon of coherence resonance can take place.