This paper examines the influence of altitude on the corona discharge and breakdown behavior of rod-plate air gaps using a two-dimensional fluid dynamics model. By simulating the discharge processes under different air pressures corresponding to various altitudes, the study provides a detailed analysis of key parameters such as electron density and electric field strength. The results demonstrate that as air pressure decreases, the voltage required for breakdown also decreases, and the discharge becomes more intense under the same voltage. The study categorizes the discharge process into three stages: no significant discharge, corona discharge, and breakdown discharge. Importantly, the presence of corona reduces the breakdown voltage below the predictions of Paschen’s law. Furthermore, the numerical results exhibit a strong correlation with Paschen’s law, confirming the model’s accuracy and reliability. These findings highlight the critical role of corona effects in influencing breakdown voltage and provide valuable theoretical insights for understanding high-altitude discharge phenomena. The outcomes also serve as a foundation for optimizing the insulation design and enhancing the performance of electrical systems operating in high-altitude environments, where reduced air density poses significant challenges to system reliability and safety.