Abstract: The present disclosure relates to a brake cylinder, a brake caliper unit and a rail vehicle. The brake cylinder includes 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, a thrust sleeve and a gap adjusting nut assembly; wherein the gap adjusting nut assembly includes 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. The thrust sleeve spring of the brake cylinder of the present disclosure can recognize excessive elastic deformation of the external lever to prevent the gap adjustment triggered by the excessive elastic deformation of the external lever, ensuring that the release gap of the disc is constant.