Abstract: The remaining coal pillars in abandoned or closed mines are not only subjected to overburden load, but also in a confined water environment. The coupling effect of the two causes the deterioration of the mechanical properties of coal pillars, which in turn affects the stability of coal pillars and overburden. In order to study the deterioration characteristics and mechanism of mechanical properties of coal rock after the coupling effect of load-pressure water immersion, firstly, based on the self-developed coal rock pressure water immersion test system, coal samples with different load-pressure water immersion coupling effects were prepared ( among them, the axial loads were 0, 3, 5 and 8 MPa, respectively, and the immersion pressure was 2 MPa). Secondly, the structure and composition variation characteristics of coal samples before and after coupling were obtained by using rock computer tomography (CT) three-dimensional imaging scanner and X-ray diffraction (XRD) instrument. Then, combined with the three-dimensional full-field strain measurement system, acoustic emission monitoring system and scanning electron microscope, the uniaxial compression test of coal samples after load-pressure water immersion coupling was carried out to study the strength, macroscopic failure, acoustic emission, meso-characteristics of fracture and energy evolution characteristics of coal samples. Finally, the deterioration mechanism of mechanical properties of coal rock under load-pressure water immersion coupling is revealed. The results show that compared with that before the coupling effect of load-pressure water immersion, with the increase of axial load, the porosity of coal sample ( the aggregate of pores and cracks in coal sample ) increases as a whole after the coupling effect of load-pressure water immersion. At the same time, the proportion of kaolinite and illite in clay mineral components of coal sample decreases step by step, and the damage variable of coal sample increases. Taking the coal sample with axial load of 8 MPa as an example, its porosity increased by 91.1%, kaolinite and illite content decreased by 64.4% and 81.0% respectively, and the damage variable increased to 8.71%. With the increase of axial load, the uniaxial compressive strength and elastic modulus of coal samples show a decreasing trend, and the local evolution of overall deformation is significant, accompanied by active acoustic emission signals. The macroscopic damage degree of coal samples is severe, and its fractal dimension is relatively large.The porosity and probability entropy at the fracture surface of coal samples increase with the increase of axial load. Compared with that before the load-pressure water immersion coupling, the average porosity and probability entropy of coal samples with axial load of 8 MPa increase by 209.7% and 4.0%, respectively. In addition, with the increase of axial load, the pre-peak elastic energy and post-peak surplus energy of coal samples decrease ; the coupling effect of load-pressure water immersion causes damage to the coal sample, which deteriorates its mechanical properties. When the axial load is small, the pressure water-coal-rock interaction becomes the dominant factor for the deterioration of mechanical properties of coal samples, which is caused by the argillization and dissolution of hydrophilic clay minerals in coal samples. With the increase of axial load, the coupling effect of load-pressure water immersion is improved, and due to the lubrication effect of pressure water immersion, the larger axial load is more likely to drive the crack connection and penetration of coal samples, and even cause some areas to fall off in blocks. Both of them aggravate the deterioration of mechanical properties of coal samples, resulting in a decrease in strength and a relatively significant deformation and failure characteristics.