To provide a method for estimating particle size distribution of soil capable of accurately estimating the particle size distribution of soil containing small particles by machine learning with artificial intelligence.SOLUTION: Particle size distribution of collected soil is estimated with a trained model 20 (see Fig. 3) that is obtained by machine learning with artificial intelligence built into a server 11 using, as training data, a large number of images of soil in each single particle size that was screened from raw material soil and classified into a plurality of particle sizes. The images of soil in each single particle size used as the training data is an image of the surface spread with a predetermined thickness T that is captured by a photographing device 12 and linked with each classified particle size. The image, which is obtained by capturing the image of the surface of the collected soil spread with the predetermined thickness T by the predetermined photographing device 12, is input to the trained model 20 to estimate the particle size distribution of the collected soil by outputting a ratio of each classified particle size of the collected soil.SELECTED DRAWING: Figure 1