The invention discloses an external connection-preventing short message control device for an internal network computer. The external connection-preventing short message control device comprises a USB main board connecting head, a relay, a logic control module, a GSM module, a voltage-stabilized source and a concentrator, wherein the USB main board connecting head, the relay and the concentrator are sequentially connected, and the concentrator is connected with a plurality of USB interfaces; the logic control module is connected with the GSM module and the relay, respectively, and the voltage-stabilized source is connected with the logic control module and the GSM module, respectively. According to the external connection-preventing short message control device for the internal network computer, the secret divulging or illegal external connection of the internal network computer can be effectively avoided; the external connection-preventing short message control device can be widely applied to computers in each transformer substation and office space of State Grid Corporation of China, also can be widely popularized and applied to other departments with security demands and is simple and practical in structure and stable and reliable in performance.