Abstract: Taking 3304 working face of Zhaozhuang Coal Mine No.3 coal bed as the research object, using UDEC simulation method, damage movement and deformation of overlying strata and the distribution of mined out area porosity is studied. The results show that the strata subsidence form is similar to “dustpan” shape distribution. The quantitative expression of porosity distribution and the distribution of porosity are obtained. With the increase of height, the porosity of the falling rock mass decreases gradually.