A non-contact method of measuring the body size of pigs based on stereo-infrared images was established to address the issues of common color images easily affected by environmental lighting and depth images prone to producing holes in the process of measuring the body size of pigs. Infrared images were used to extract foreground of pigs. Ellipse fitting and projection difference methods were used to segment the head and tail of pig. Convex hull analysis and symmetry testing methods were used to select the ideal posture of the pig. Stereo images were used to obtain depth information of the pig， and a homography matrix was used to fuse the advantages of both the infrared and stereo images. A method of measuring the body size of pigs was designed based on these. The results showed that the contours of the pig extracted from the infrared images were clear and smooth. The algorithm of selecting ideal posture had an accuracy of 94.0%. The average relative error of the measurements for body length， body width， hip width， body height， and hip height was 1.78%， 3.26%， 3.20%， 1.92%， and 2.27%， respectively， with an overall average relative error of 2.49% and an average absolute error of 1.42 cm. It is indicated that the algorithm proposed meets the requirements of accuracy for measuring the body size of pigs. It will provide a feasible solution for continuously and automatically measuring the body size of pigs.