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This paper describes a systematic method with high accuracy and efficiency to scientifically analyse the long-term stability and deformation behaviour of an anhydrite mine-out located in Anhui, South China and evaluate the feasibility of this mine-out as an underground crude oil storage space. Applying the particle swarm optimization algorithm, the parameters of Burgers creep model of anhydrite rock were obtained based on the uniaxial compressive creep test. Considering the results of numerical simulation, element safety factor (Esf) based on the Mohr's strength theory was introduced and modified to quantificationally evaluate the long-term stability of cavern group. Combining field monitoring, the long-term deformation behaviour of the mine-out was analysed. The results show that the mine-out has good long-term stability and non-deformability. After 100 years of natural deformation, the vertical convergence deformation of the cavern is less than 500 mm, while lateral convergence deformation is less than 450 mm. The ground settlement is not more than 234 mm. The maximum loss rate of the space volume is no more than 5.38%, which is 4.75% under the condition of crude oil storage with 1.0 MPa internal pressure. Therefore, the mine-out has the potential to serve as an underground crude oil storage space. [ABSTRACT FROM AUTHOR]