The superconducting electrodynamic suspension(SC-EDS) train exhibits significant advantages such as levitation and guidance self-stabilizing, large levitation gap, and high lift-to-drag ratio, indicating promising applications in high-speed and ultra-high-speed maglev rail transportation. This paper addresses the longitudinal upper and lower limit speed protection issues of the SC-EDS train, defining and proposing computational methods for upper and lower limit speed protection curves. Inspired by the safety protection strategies of wheel-rail and the electromagnetic suspension (EMS) train, and considering the two-stage braking process involving suspension and landing phases, this research establishes the upper-limit speed protection curves and the lower-limit speed protection curves. The methods for calculating these protection curves are elaborated, taking into account adverse conditions and equipment response delays.