Abstract: In order to accurately determine the depth of coal seam floor failure and the factors affecting the depth of failure, we take the 12304 thick coal seam fully mechanized caving working face of Wangjialing Mine as the engineering background, and use 3DEC discrete element numerical simulation software for simulation.The plastic failure zone range of the simulation results is analyzed, and the depth of failure of the 12304 working face floor is about 20.6 m.By comparing empirical formulas and conducting on-site measurements using the strain method, the value is within the range of on-site monitoring results, verifying the accuracy of the numerical simulation results.At the same time, numerical simulation was used to study the influence of different inclined lengths and mining heights of the working face on the plastic failure of the floor.The study showed that the depth of floor failure was positively correlated with the mining height and inclined length of the working face.The research results can provide basic data for the evaluation and prediction of water inrush from coal seam floor, as well as technical basis for formulating targeted water prevention and control measures.