The embodiment of the invention provides a method for automatically identifying organs endangered by radiotherapy in a CT image based on a deep semantic network. The method comprises the following steps: S1, preprocessing a CT three-dimensional image; s2, obtaining a part to which each two-dimensional image in the CT three-dimensional image belongs; s3, respectively constructing deep semantic segmentation models for the pelvic cavity, the abdomen, the chest, the head and the neck; s4, inputting the two-dimensional images belonging to the pelvic cavity, the belly, the chest, the head and the neck into a trained deep semantic segmentation model for the corresponding pelvic cavity, the belly, the chest, the head and the neck to identify organs endangered by respective radiotherapy; and S5, combining results output by the deep semantic segmentation models of the pelvic cavity, the abdomen, the chest, the head and the neck. According to the method, artificial intelligence-assisted radiotherapy endangered organ contour sketching is implemented in the working process of radiotherapy planning, preoperative evaluation of surgical operation and operation planning, and the working efficiencyof medical workers can be effectively improved.