Combined with the practical needs of daily life, the article designs a monocular distance measurement system based on face recognition. The system first uses the camera to capture video images, thresholds the face part of the image through image processing, trains a strong classifier based on the improved Adaboost algorithm and cascades it to achieve face detection and obtains the width information of the face image, determines the coordinate relationship of the target position relative to the camera, and uses the geometric similarity principle of small-aperture imaging according to the construction of a distance measurement model that meets the demand. The distance between the target person and the camera is calculated using the pixel information of the face image and the actual face width relationship, and finally, the obtained detection information is presented through the GUI visualization interface. The experimental results show that the system has high accuracy and good stability, and has good feasibility and application prospects.