Abstract: When the upper part of coal-bearing strata is covered by the thick unconsolidated layer, the boundary area of the subsidence basin induced by coal mining exhibits a distinctive phenomenon of range expansion and slow convergence. In order to fully understand the evolution characteristics of mining surface subsidence in the outer boundary area of subsidence basin, and build the surface subsidence prediction model under the thick unconsolidated layer. Taking the 13121^up working face of Gubei Coal Mine as an example, the dynamic evolution process of surface subsidence convergence effect the outer boundary area of subsidence basin and its range expansion are analyzed using the measured data, and the correlations between surface subsidence characteristics and geological mining conditions are investigated. On this basis, the influence mechanism of unconsolidated layer thickness on surface subsidence characteristics is revealed. Then, the modified surface subsidence prediction model is proposed by integrating the Logistic function, and the parameters inversion method of the modified prediction model is proposed based on the whale optimization algorithm. Finally, the impact of geological and mining conditions on the new parameters of the modified model is discussed. The results show that the surface subsidence convergence in the outer boundary area shows a clear segmented nature, and the convergence effect in the fast convergence zone rapidly converges and then slows down as the mining degree increases, the outer boundary area expansion undergoes a process of sharp expansion, then steady expansion, and finally slight contraction. The maximum surface subsidence value, the slope of subsidence convergence effect coefficient in the fast convergence zone, and the outer boundary area expansion range are linearly correlated with the buried depth, mining height, mining degree coefficient and the proportion of unconsolidated layer in the overlying rock. The additional subsidence caused by the full compaction of broken rock, the reduction of mining subsidence consumption, the compression of unconsolidated layer medium and the consolidation of aquifer water loss is the main reason for the special subsidence phenomenon of boundary area in the thick unconsolidated layer subsidence basin. The modified surface subsidence prediction model can effectively solve the problem that the predicted results of the probability integral model converge too fast in the outer boundary area while restoring the actual physical significance of the subsidence coefficient q. The new parameters of the modified model gradually decrease with the increase of unconsolidated layer proportion and burial depth, and fluctuation increase with the increase of mining degree coefficient, but are not significantly affected by the changes of mining height. The application of the modified prediction model to the engineering practice of the 13121^up working face of Gubei Coal Mine has achieved good results. These research results will provide a scientific basis for the coal mining design under buildings, water-bodies and railways in the thick unconsolidated layer condition, and promote the coordinated development of resource exploitation and farmland protection in the area where coal and grain coexist in Huainan and Huaibei.