Cabin pressure altitude warning function is an essential function for civil aircraft pressurization system to remind pilots the cabin pressure altitude is beyond safe limit. It is required by airworthiness standard that there should be a warning message at the pilot to indicate the cabin pressure altitude exceeds 3048 m(10000 ft). However, most plateau airports are above 3048 m(10000 ft). Most types of aircraft require pilots to manually set the warning threshold to avoid false warning, which has some disadvantages. This article provides a new design method for cabin pressure altitude warning function which can automatically set the cabin pressure altitude warning threshold on plateau airport route.