In order to solve the problems of large number of operators, large labor intensity, and large influence of human factors in the flattening process, designed the spherical (flat) propellant automatic flattening process. Through the description of the automatic flattening process, the particle image sampling device is designed based on the principle of flattened grains particle sampling and arc thickness automatic measurement, and the smallest outer rectangle is used to extract the pixel thickness of the particles, and the automatic measurement software for the flattened drug particle arc thickness is built, realize automatic adjustment of flattening roller distance, online sample collection and automatic arc thickness measurement. The results show that the design reduces the number and labor intensity of the flattening process, and has practical significance for improving the safety and quality control level in the production of propellant.