Spherical fiber filter is an important water purification device under the coal mines. When the thickness and porosity of its internal filter layer changes, the filtering performance will also change. In order to study the effects of the filtration performance of the porosity and the thickness of the lower filter layer, this article uses SolidWorks for modeling and ANSYS CFD (Computational Fluid Dynamics) numerical simulation technology for simulation analysis. The conclusion is obtained through simulation research: The filter layer porosity above the fiber filter is 0.7, the porosity of the filter layer below is 0.6, And when the filter layer thickness of the porosity of 0.6 accounts for 30% of the thickness of the entire filter layer, the filtering performance is the best. At this time, the pressure drop in the filter will not be too large, causing too much energy loss. And the filtration speed will not be too small and cause too low efficiency.