The failure law of weak overburden stratum is an important factor affecting the safe mining of coal. A com⁃ prehensive method including field investigation，theoretical analysis，numerical simulation was applied to investigate the failure law of weak overburden stratum underlying extra⁃thick alluvium based on the geological conditions of the 3301 working face of the Guotun coal mine in the Juye mine area. The results were obtained as follows:1 This paper re⁃ veals the mechanical evolution process of weak overburden stratum underlying extra⁃thick alluvium，illustrates the com⁃ prehensive influence mechanism of alluvium thickness，bedrock and their linkage evolution，and proposes the method to predict the height of weak overburden stratum failure based on the plastic fracture characteristics. 2 The failure form and fracture development and expansion law of failure law of weak overburden stratum underlying extra⁃thick alluvium are clarified，and the development of failure law of weak overburden stratum successively experiences three stages: slow growth stage，rapid growth stage，and stability stage. The influence mechanism of loose layer thickness and mining height on the failure of weak overburden is analyzed. The height of weak overburden stratum has a linear relation⁃ ship with the mining height，an exponential function relationship with the thickness of alluvium，and the correspond⁃ ing mathematical expressions are fitted based on a regression analysis method. 3 The results of the downhole segmen⁃ ted water injection method show that the failure height under the conditions of extra⁃thick alluvium(515 m)，weak o⁃ verburden stratum and large mining height(6 m) is 78 m，which is 13 times of the mining height，and developed into the mudstone rock strata. The theoretical analysis and numerical simulation results are verified based on the wa⁃ ter hazard analysis，water inflow and stope ground pressure law of the working face.