An anti-theft device comprises a support, a gear component clamped with the support, a spring connected with the support and a chute which is connected with the support in a sliding manner, wherein the center of the support is provided with a through hole and/or lockhole; and the gear component contains a stud, a straight gear, a position-blocking gear and a linkage shrapnel clamped with the position-blocking wheel, wherein the straight gear and the position-blocking gear are sleeved on the stud in turn. In the anti-theft device and an anti-theft projector, the support fits with the gear component to push the support out under the elastic force of the spring, thus the through hole on the support can be directly fixed with a curb chain or the lockhole on the support can be directly fixed through a latch and the aims of security and theft resistance can be achieved.