A quick release device of a brake cylinder includes: a first support iron plate; a second support iron plate installed with an interval from a side of the first support iron plate; an iron plate ejector, installed between the first and second support iron plates, for expanding the relative distance between the first and second support iron plates; a wrench assembly, sheathed on the iron plate ejector in a quick release status; and at least one quick release portion, installed at a relative position of the iron plate ejector and the second support iron plate, so that the second support iron plate is in a quick release status.