Nowadays, more and more problems of environmental deterioration make the development of environmentally friendly energy imminent. For the requirements of low cost, high security, and high efficiency, aqueous Zn-ion batteries are a promising trend for research. In this paper, the mechanism of aqueous Zn-ion batteries will be illustrated in three aspects: cathode materials, zinc anode, and electrolytes. Moreover, possible alternatives for each part of the batteries will be comprehensively illustrated in detail. In addition, the challenges such as short capacity, zinc dendrites, and corrosion and passivation will be analyzed and the possible corresponding solutions will be proposed. Finally, a concise conclusion will be given.