The aim of this paper is to present a theoretical derivation of an end stop design in linear synchronous permanent magnet generator, utilized in a wave energy conversion system. To ensure a stable and proper design of the mechanical system and avoid a great impulse force in the hull, the upper end stop shall smoothly decrease the velocity of the translator to zero if the wave amplitude is larger than the stroke length. As the upper end stop, the spring, compresses, the downward force in the system is no longer only represented by the translator’s and buoy’s masses, but also the reaction force of the spring. The buoy exposes a greater downward force and submerges further down in the water. A relative motion between the wave and buoy occurs, an important parameter when the upper end stop shall be designed