A brake cylinder, comprising a cylinder block and a cylinder head fixedly sleeved over one end of the cylinder block, the cylinder block being provided therein with a piston, a guide spring, a guide nut, a taper sleeve, an adjusting shaft assembly and a gap adjusting nut assembly, wherein the gap adjusting nut assembly comprises a gap adjusting nut, a gap adjusting sleeve and a gap adjusting spring, and a groove extending along an axial direction of the gap adjusting sleeve is formed on an outer circumferential surface of the gap adjusting sleeve, in which groove a release gap adjusting unit is provided.