<p>To enhance the long-term strength assessments of water-bearing rocks under stress relaxation conditions by stress relaxation tests at different water content, pore-water pressure, and confining pressure, we delve deeply into the stress relaxation characteristics of sandstone, thereby improving the method for determining long-term strength. The results indicate that: The rock’s modulus of elasticity decreases while the Poisson’s ratio increases as water content and pore-water pressure increase. The characteristics of rock stress relaxation become pronounced during the phase of crack extension. Furthermore, an increase in confining pressure, pore-water pressure, and water content serves to intensify the degree of stress relaxation. In investigating the laws governing radial deformation during rock stress relaxation, it is more precise and scientific to employ the traits of radial strain variations as criteria for demarcating stress relaxation phases. The radial deformation can also be used to distinguish rock’s pre-peak or post-peak states. An improved method for determining the long-term strength of rocks by investigating the deformation inter-conversion characteristics at different stages of rock stress relaxation, achieving an accuracy of 10 percent. Understanding stress relaxation characteristics and the laws governing long-term strength under diverse water content conditions offers different insights to ensure the long-term safety and stability of engineering projects.</p>