The purpose of this experiment was to find a suitable algorithm for leaf rotation in the Litchi canopy PAR(Photosynthetically Active Radiation) simulation. Bilinear interpolation algorithm was introduced to the rotation of leaf gray pictures in this study. Pictures were also rotated with the nearest interpolation algorithm for comparison. Results were analyzed emphasizing the transition of the borderline and ratio of target area in the binary image. It showed that in the rotated images, when using the bilinear interpolation algorithm, the transition between target and background was smooth, the borderline was clear and the definition of the whole image was satisfying. By using the nearest interpolation algorithm, the definition of the rotated image was not so satisfying that there were diamond effects on the borderline of target and background. It also showed that there was a distortion of 20 pixels in binary image for average when using nearest interpolation algorithm.