The invention discloses a collision-prevention device for a security door. The collision-prevention device comprises a limit inner frame, a door frame, reinforcing assemblies and a door leaf, the doorleaf is installed on one side edge of the door frame, the limit inner frame is arranged inside the door frame, and two sets of symmetrical reinforcing assemblies are arranged inside the limit inner frame; the reinforcing assemblies comprise first collision-prevention frames, reinforcing tightening latches, second collision-prevention frames, second fixed clamping grooves, installing plates, through holes, rubber washers and first fixed clamping grooves, the first collision-prevention frames and the second collision-prevention frames are symmetrically arranged, and the first fixed clamping grooves are formed in the first collision-prevention frames. Through the design of the reinforcing assemblies, the reinforcing assemblies are distributed on and installed on the periphery of the door frame, the reinforcing tightening latches are installed among the reinforcing assemblies, when someone tries to impact and destroy a door plate in real time, external impact force can be dispersed, the anti-impact performance of the door leaf is strengthened, and the whole intensity of the security door is improved, so that the collision-prevention performance is improved.