The dynamics boundary and its protection strategy for landing when aircraft system failure occurs is studied.The longitudinal dynamics model of an aircraft under system failure is established with a certain transport aircraft as the research object.To solve the problem that the failure of the system may lead to loss of control in flighta dynamics boundary determination method based on the reachability set theory is proposedand then the situations of elevator jamming and thrust loss are analyzed respectively.In order to ensure the safety of landing under system failurea dynamics boundary protection system is designed and the effectiveness of the system is verified through dynamics simulation.The research results can provide a new idea for the design of boundary protection systems for aircraft landing.