The invention relates to a reliable locking method of an electric actuating cylinder, relating to the technical field of mechanical structures. According to the scheme provided by the invention, an undercarriage provides power for retracting and getting off, a built-in locking mechanism provides a reliable locking force, the electric actuating cylinder can be reliably locked when bearing pulling force and pushing force in a stretching state, and is not interfered by external forces, so that the reliability of an undercarriage system is improved, and the safe lifting of an airplane is guaranteed.