The invention provides a variable ship length type wave energy underwater vehicle. The variable ship length type wave energy underwater vehicle comprises a wave energy underwater vehicle body, whereinthe wave energy underwater vehicle body comprises a ship body, a hydrofoil which is mounted at the lower part of the ship body through a support, and a rudder which is mounted at the tail part of theship body; the ship body comprises three parts, namely, a head section, an intermediate section and a tail section; and the intermediate section is a telescoping section. According to the variable ship length type wave energy underwater vehicle, the length of a ship in the sea with different wave conditions can be controlled; compared with a fixed ship length type wave energy underwater vehicle,the variable ship length type wave energy underwater vehicle has the advantages that the ship length can be properly changed so as to improve the wave energy utilization efficiency of the wave energyunderwater vehicle; in case of a long wave height condition, the ship length can be increased in order to increase the longitudinal swinging and heaving range of the ship, and as a result, the propelling performance of the underwater vehicle can be improved; in case of a short wave height condition, the ship length can be decreased to reduce the rotating inertia, thus the ship body moving range isexpanded, and as a result, the wave energy can be effectively utilized to propel.