Abstract: With the clarification of strategic positioning of hydrogen energy, the value of alkaline water electrolysis for hydrogen production driven by renewable energy sources has become increasingly prominent. Due to the complex process mechanisms and the fluctuating characteristics of input power sources such as wind and solar power, the alkaline water electrolysis system is prone to hydrogen and oxygen crossover, which affects the purity of hydrogen production and even poses safety risks. Therefore, based on the mechanism of gas impurity crossover, this paper considers both operational conditions and physical structures of alkaline water electrolysis systems, and constructs a simulation model for the volume fraction of hydrogen in oxygen at the outlet of the cooler on the oxygen side. Through local and global sensitivity analyses, the influence effects of factors under different steady and dynamic operating conditions are quantified, and, the strong key parameters affecting the hydrogen purity are sorted out. The research findings can provide a basis establishment of the operating boundary of the alkaline water electrolysis system, and guide the development and optimization of subsequent operational strategies, possessing engineering application value.