A fixing mechanism includes a base, a movable hook and a sliding key. A first end of the movable hook is for fixing an accessory. The sliding key is slidably installed on the base. The sliding key includes a key body whereon a sliding slot is formed, and a driving part for pushing a second end of the movable hook when the key body moves in a first direction so as to separate the first end of the movable hook from the accessory. The fixing mechanism further includes a rotary arm. A first end of the rotary arm is rotatably installed on the base, and a second end of the rotary arm is slidably installed inside the sliding slot. The second end of the rotary arm stops the second end of the movable hook in a closed position for preventing the movable hook from moving in the first direction.