Mixed-mode oscillations (MMOs) are a type of complex oscillation mode produced in dynamical systems. They are widespread in nature. Mixed-mode oscillations are made up of a series of small amplitude oscillations and large amplitude of the oscillations, and these two types of oscillations appear alternately. Mixed-mode oscillations in the neuronal system are introduced in this research. The effect of geometric singular perturbation theory on the generating mechanism of mixed mode oscillations in dynamic systems is mainly analyzed, and the research on dynamics of mixed-mode oscillations in the Pre-BotC neural network, stellate cells of entorhinal cortex neurons, pituitary cells and gland cells is also introduced. Additionally, the investigation on mixed-mode oscillations of other neuronal models are briefly presented. All the works will provide a good foundation on further research on mixed mode oscillations of neuronal models in the future.