The invention discloses a three-dimensional head testing method based on a single camera module for radiotherapy. The method comprises the following steps: step 1, acquiring a three-dimensional head image according to a CT scanning result of a patient before radiotherapy; step 2, acquiring a face image in real time during radiotherapy; step 3, calculating the current relative distance and the inclination angle between face and the camera module according tothe three-dimensional head image in the step 1 and the face image in the step 2; step 4, constructing three-dimensional coordinate points of a head in real time by taking the center of a camera sensor of the camera module as an original point. The face is shot by the single camera module, data of key points of the face is acquired, a rotation angle is obtained with an affine transformation algorithm, and a rotation matrix is obtained; a translation vector of the head can be obtained through combination with the three-dimensional CT image in DicomRT; three-dimensional positional information, including three-dimensional positional information of internal tumor, of the head in real space can be obtained in real time through actions of the rotation matrix and the translation vector on the three-dimensional CT image of the head, so that a tumor area is irradiated precisely by radioactive rays.