In view of the engineering example of mining under the residual ultra-wide coal pillar, the influence of residual ultra-wide coal pillar on the mining of lower coal seam was elaborated from four aspects including the loading condition and stability of coal pillar, the distribution of vertical stress under the coal pillar, the change of mining pressure and the change of roof structure under the coal pillar. Through the analysis of the existing mining pressure data and the numerical simulation analysis, the influence of the residual ultra-wide coal pillar on the weighting of the lower coal seam and on the hydraulic support working resistance in the lower coal seam were obtained. Through mechanical calculation, the calculation formula of the hydraulic support working resistance of the lower coal seam under the influence of coal pillar was obtained. And through sensitivity analysis, the concrete influence of coal pillar on multiple support and point support fracture block structure model was got.