To explore the macroscopic mechanical properties and failure evolution mechanism of desulfurization gypsum fly ash flowable lightweight soil, a numerical model of desulfurization gypsum fly ash flowable lightweight soil was constructed by PFC2D, and the microscopic parameters of the model were derived through indoor uniaxial compression tests.By extracting the types, quantities, ages and particle displacement trends of discrete crack networks in numerical models, the morphological characteristics and propagation evolution of cracks in desulfurization gypsum fly ash flowable lightweight soil were explored.And the destructive properties of desulfurization gypsum fly ash flowable lightweight soil materials were evaluated through energy indicators.The results indicate that the constructed discrete element numerical model can effectively simulate the stress-strain curves and failure characteristics of materials. Under uniaxial compression conditions, desulfurization gypsum fly ash flowable lightweight soil undergoes microcracks dominated by shear failure at the initial stage of loading. When the loading exceeds the peak stress, through cracks dominated by tensile failure occur. The solidified soil particles of desulfurization gypsum and fluidized fly ash gradually show a horizontal displacement trend from vertical displacement. The evolution of dissipated energy in desulfurization gypsum fly ash flowable lightweight soil is relatively gentle, and its corresponding macroscopic manifestation is that there is a certain degree of delayed cracking in the failure of fluidized fly ash after exceeding the peak stress point.