The invention provides a method for synthesizing a face backlight picture. The method comprises the following steps: S1, preprocessing an image; s2, face feature point detection: S2.1, a normal face image is sent to a face detection model, and face contour points are detected; s2.2, inputting the background image into a face detection model, and detecting background face contour points; s3, generating a closed face contour line; s4, mask construction: S4.1, applying a flooding filling algorithm to the image template M to generate a face region mask 0; s4.2, according to the corresponding contour points, solving homography matrixes of the two images; homography transformation is carried out on the mask0; a mask 1 after transformation is obtained; homography transformation is carried out on the face image; a transformed face image is obtained; s4.3, carrying out negation operation on the mask 1, and generating a background region mask 2; s5, target area extraction: S5.1, performing mask operation on the transformed face image and a mask 1, and extracting a face area to obtain an image I1; s5.2, performing mask operation on the background image and a mask 2, and extracting a backlight background area to obtain an image I2; and S6, image splicing: carrying out addition operation on the obtained image pixels to obtain a spliced image.