Abstract: Under the long-term influence of water, the mechanical properties of coal pillar in goaf will be weakened and the overburden migration will be induced.In order to investigate the damage deformation and failure process of coal pillar immersed in water in the goaf, the influence of water accumulation in the goaf on the stability of overlying rock and the mechanical properties of coal pillar under strip mining conditions is studied based on similar simulation test.By monitoring the migration of overlying rock and the stress change of coal pillar, the phenomenon of “activation” failure of overlying rock is discussed.The influence of soaking time on the elastic modulus, peak strength and other mechanical properties of coal samples was analyzed by mechanical property test.The results show that with the increase of water accumulation time in the goaf, the coal pillar undergoes water immersion softening, leading to mechanical strength degradation, and then leads to shear failure and “activation” movement of overlying rock.The movement deformation of overlying rock near the goaf presents the characteristics of a wavy subsidence basin.The damage effect of water immersion significantly reduces the elastic modulus and peak strength of coal sample, and there is an inverse relationship between the time of water immersion and the mechanical properties of coal sample.