Abstract: In order to achieve the safe mining of deep coal resources under high pressure, considering that the top of Ordovician limestone in southern Shanxi some mining areas has the significant certain water resistance,the technical idea of increasing the thickness of the coal seam floor aquitard has became an important solution in the prevention and control of Ordovician limestone water. Taking the top of Ordovician limestone in Wangjialing Coal Mine as the research project,the water resistance performance was studied through mechanical property testing,scanning electron microscopy,mercury intrusion testing, permeability testing,and other methods. Research has shown that within the top thickness of 0 m to 20m range of the Fengfeng Formation in Wangjialing Coal Mine,the rock uniaxial compressive strength was within 37. 32 MPa to 63. 34 MPa,the rock permeability was ranged from 1. 21×10^-5 μm² to 9. 92×10^-4 μm²,and the rock permeability coefficient was within 1. 16×10^-8 to 5. 99×10^-7 cm/s. The results show that, for the ordovician top, the rock uniaxial compressive strength is high, the connectivity between pores is poor the degree of pore development is low the permeability performance is poor, and the permeability grade belongs to the extremely micro permeable type. The Ordovician top can be considered as a relatively impermeable layer.