The invention discloses a system and method for automatically controlling sugar boiling through high-definition-video online detection. The automatic control system comprises a detecting device and a computer video control device, and the detecting device is provided with a high definition camera capable of obtaining dynamic real-time images of contents in a sugar boiling tank. The automatic control method includes the following steps that 1, a light-source distributor and a mirror-face cleaning device are installed in the sugar boiling tank, and detecting glass is embedded to the wall of the sugar boiling tank; 2, the state of the contents in the sugar boiling tank in the syrup stage, the state of the contents in the sugar boiling tank in the seed-crystal stage and the state of the contents in the sugar boiling tank in the crystal stage are monitored in real time through the high definition camera; 3, the collected dynamic real-time images are transmitted to the computer video control device through the high definition camera, and the images are subjected to data transformation , statistics and analysis through the computer video control device; 4, an early warning is carried out when the quality control standard is not met. According to the automatic control system and method, the real-time dynamic images of the contents in the sugar boiling tank are monitored, and valuable real-time parameters are provided for the sugar-boiling crystallization process.