An automatic shooting mechanism capable of remote switching and unmanned switching between a safety mode and a shooting mode, and remote shooting and unmanned shooting. Also provided is a sentry robot employing the automatic shooting mechanism and capable of performing wide and narrow monitoring and sentry duties in short and long ranges, and automatically shooting at a target. The automatic shooting mechanism comprises a safety unit including a safety solenoid and an elastic member to move a safety pin of a gun between a safety mode position and a shooting mode position, and a return unit for applying force to the safety pin of the gun to move the safety pin to the safety mode position. The automatic shooting mechanism further comprises a shooting unit including a shooting solenoid to move a connecting link back and forth, and a trigger push member having one end contacting a trigger of the gun and the other end contacting the shooting solenoid, and coupled at a middle portion of the shooting unit to be capable of pivoting to pull the trigger as desired.