A protective sheath comprises a rear plate, a front plate and a wireless HMI device comprising a main portion embedded inside the rear plate, a human-machine interface embedded inside the front plate and a soft flat cable electrically connecting there-between. The front plate comprises a first folding plate, a holding component for holding a portable electronic device on the first folding plate, a position limiting hinge, and a second folding plate pivoted to the first folding plate via the position limiting hinge. Hence, the first and the second folding plates can cover a rear surface of the portable electronic device together by being relatively unfolded, and are maintained at a presetting pivoting angle by the position limiting hinge after being relatively folded. The front plate can be folded relative to the first folding plate to cover a display surface of the portable electronic device.