Based on modeling and analysis, this paper applies for achieving requirement analysis and proposal design for dehumidification system of civil aircraft. Firstly, geological and thermal transfer models are set up based on cabin vertical section. Secondly, relationship between saturated humidity and temperature is analyzed to capture dehumidification requirement. Thirdly, comparing requirement and relative parameters on typical aircraft cruise condition, dehumidification system design is proposed. Lastly, the quantities of components applied on real aircraft, analysis and design rationality is demonstrated.