Abstract: To study the pressure unloading effect of lower coal seam under upper protective layer in the mine with the depth over 1 000 m, YHW19 mine-used intrinsically safe roof and floor displacement monitor is used to monitor the swelling deformation of the underlying Ji₁₅ coal seam, which is based on the Ji₁₄-31070 working face buried in No.12 coal mine with the depth over 1 000 meters. The results show that with the advance of the Ji₁₄ protective layer, the swelling deformation of the lower seam Ji₁₅ has experienced a slow growth in the early stage, the rapid growth in the middle period and the stable stage in the later period, and the area of 15 m to 45 m away from the mining face is the main influence area of protective seam mining pressure unloading. The swelling deformation of the protected seam in this area is significantly affected by the change of mining speed. The average value of maximum swelling deformation of Ji₁₅ coal seam is 22.4 mm, and the average value of maximum swelling deformation is 6.82‰. The protected layer is fully unloaded. The data point fitting shows that the swelling deformation of coal seam, the gas concentration of single hole and the total gas drainage are in good accord with the growth trend of the three times polynomial with one element in the whole monitoring period. The effect of pressure unloading is obvious and the effect of pressure unloading is remarkable.