The invention discloses an anti-theft alarm of an entrance door. The anti-theft alarm comprises a body and an alarm horn, wherein a rectangular block is arranged at one side of the body, the other side of the body extends outwards so as to form a slope, the slope and the bottom end of the rectangular block are in the same plane, the alarm horn is installed at the top of the rectangular block and is connected with a control circuit in the rectangular block, the control circuit is connected with a contact on the slope, a 15-30 degree of slope angle is formed between the slope and the horizontalplane, a press plate is formed on the slope, one end of the press plate is connected at the bottom of the slope angle, the other end of the press plate extends along the slope angle so as to enable the inner side and the contact to contact and lean against, the rectangular block is internally provided with a battery powering the control circuit, when the press plate presses the contact, the control circuit connected with the contact is on and controls the alarm horn to give out an alarm. The anti-theft alarm of the entrance door has a simple structure, is small and convenient to carry, can alarm when an intruder manages to enter the room and can prevent the intruder from pushing the door to enter forcibly, thereby gaining time for self-rescue or rescue.