The invention relates to a sliding rotating shaft mechanism and an armrest box armrest. The sliding rotating shaft mechanism comprises a sliding rotating cantilever, a sliding rotating rail support, a straight tooth one-way ratchet wheel, a left spiral spring, a check spring piece, a right spiral spring, a straight tooth coil spring protective cover, a coil spring and a two-way ratchet wheel protective cover, wherein one end of the sliding rotating cantilever is integrated onto an armrest cover plate part, the sliding rotating cantilever comprises a left arm and a right arm, the left arm and the right arm are arranged in a left-and-right spaced mode, the sliding rotating rail support comprises a left sliding rotating rail and a right sliding rotating rail, and the left sliding rotating rail and the right sliding rotating rail are arranged in a left-and-right spaced mode. Linear rails and rotary rails are adopted, the armrest slides linearly and then move rotatably through matching of the ratchet wheel, gears, toothed rails, springs and the like, and therefore limits of the mechanism on armrest modeling and spatial arrangement are reduced; the armrest achieves the functions of damping and stagnation close to any position, and can achieve the function of automatic returning of the mechanism.