Abstract: Al-based silicon carbide (SiC) composites serve as the core substrate for space microwave component packages due to their high thermal conductivity, low coefficient of thermal expansion, and excellent dimensional stability. However, their hydrogen desorption in confined spaces easily causes "hydrogen poisoning" of hydrogen-sensitive chips, seriously impairing device reliability. Existing research lacks clarity on how hydrogen partial pressure affects the material’s desorption rate in such environments. To address this gap, this study investigates the hysteretic hydrogen desorption characteristics of Al-based SiC composites under pressure, establishing a corresponding theoretical framework. Two chambers (cubic/flat) with identical internal surface area but 11.5x volume difference were designed, and desorption rates were measured via dynamic pumping and static pressure rise methods. A hysteretic hydrogen desorption factor was defined to quantify the inhibitory effect of hydrogen partial pressure, with theoretical validity verified by comparing simulations (based on a recombination-dissociation limited model accounting for readsorption) with experimental data. Results show that increased hydrogen partial pressure significantly inhibits desorption: when the hydrogen partial pressure in the flat chamber reaches 25.64 Pa, the desorption rate drops to 26% of the unperturbed level, demonstrating obvious hysteretic behavior. The model accurately predicts desorption rate and hysteretic factor variations. This study offers key theoretical and experimental support for hydrogen control design and reliability optimization of space microwave component packages.