The present invention discloses an automatic alarm system and method used for monitoring children safety which is applied to a children monitoring terminal. The method comprises the steps of when the children monitoring terminal is turned on to enter a working mode, shooting the human body images of the children by a shooting device of the children monitoring terminal; detecting whether the human body images contain the specific characteristics, when the human body images contain the specific characteristics, starting a positioning unit of the children monitoring terminal to position the geographic position information of the children; generating a human body image alarm message containing the concrete geographic positions of the children and the specific characteristics; automatically sending the alarm information to a police monitoring center platform to alarm via a communication unit of the children monitoring terminal. The automatic alarm system and method used for monitoring the children safety of the present invention can position the concrete positions of the children accurately on the unsafe conditions that the children get lost, are abducted and trafficked, are kidnapped, etc., can help the children send out the help information in the first time, and enables the polices to rescue the children in the first time.