In order to study the dynamic mechanical properties and failure laws of coalmine rock material under passive confining pressure conditions, Ø50 mm variable cross-section split Hopkinson pressure bar (SHPB) apparatus was used to conduct impact compression tests in different loading rates with 45 # steel sleeve providing constraint conditions. Test results show that ductility and damage resistance of rock material increase under passive confining pressure. The failure axial stress of rock specimens under passive confining pressure is about 1.2 times as large as that without passive confining pressure. And its failure strain is also about 1 to 2 times bigger than without passive confining pressure. The radial stress increases with axial stain growing. The failure mode for rock specimens with or without passive confining pressure is different, with passive confining pressure is compression-shear mode.