The invention relates to a shaft-end seal test device for a high-speed decelerator. The device comprises a main shaft which is connected with a high-speed motor to form a drive end and is arranged in a horizontal direction, and two sets of shaft-end seals disposed on a sleeve of the main shaft. The periphery of the main shaft is provided with an annular sealed cavity which is disposed on the pedestal and is located between the two shaft-end seals. The main shaft is also provided with a bearing located in the sealed cavity. The peripheral surfaces of the shaft-end seals are sleeved by adjustment flanges. One end, far from the sealed cavity, of each shaft-end seal is provided with a lubricating oil leakage receiving disc. The device also comprises an adjustment mechanism which adjusts the flanges to move in the axial direction of the main shaft so as to simulate the radial jump of the shaft-end seals. The device can achieve a lubricating mode needed by the bearing in the sealed cavity, carries out the performance testing of the shaft-end seals at the same time in the lubricating mode, and improves the testing efficiency of the shaft-end seals. In addition, the device also can simulate the radial jump of the shaft-end seals.