Abstract: The long-term permeability characteristics, deterioration evaluation and engineering response of the Xiyu Conglomerate are important engineering problems in water conservancy and hydropower geotechnical engineering in Xinjiang, which are of great significance to groundwater resources management, engineering construction and disaster prevention in Xinjiang. In this study, the long-term seepage characteristics of the Xiyu Conglomerate was analyzed by long-term low-pressure stable seepage, accelerated seepage test and nuclear magnetic resonance test on the conglomerate of the Xiyu Conglomerate with different cementation degrees in the dam site area of the Nuer Reservoir. The test results show that the permeability characteristics of conglomerate are affected by particle gradation, pore structure and cementation composition, and with the increase of laboratory experimental time, the fine particles in the conglomerate in the Xiyu Conglomerate will spalling and loss, resulting in the increase of porosity and the gradual increase of the seepage coefficient of the Xiyu Conglomerate, showing a certain deterioration of permeability characteristics. Through the comprehensive analysis of experimental methods, it can be seen that the reason for the deterioration of the permeability characteristics of the conglomerate in the Xiyu Conglomerate is that under the action of long-term seepage, the internal cementation of the conglomerate in the Xiyu Conglomerate is gradually destroyed, and the fine particles are lost with water after falling off, resulting in the gradual increase of its permeability coefficient and porosity. The research results of this paper will provide important technical support for the anti-seepage design and construction of water conservancy and hydropower projects in Xinjiang.