The invention discloses a joint protecting device. The joint protecting device comprises a first fixing part, a first connecting part, a sliding part, a cavity and a second fixing part. The first fixing part, the first connecting part, the cavity and the second fixing part are connected in sequence, the sliding part is arranged in the cavity in a sliding mode in the direction from the first fixing part to the second fixing part, the cavity is divided into a first cavity body and a second cavity body by the sliding part, the sliding part is provided with first through holes, and the end, connected with the cavity, of the first connecting part extends into the cavity and is connected with the sliding part. The joint protecting device can prevent ligament strain and achieve ligament stretch overload protection without influencing normal motion of the human body.