Abstract: In order to solve the problem of the deviation between the conventional theoretical results and the experimental results of the suspension velocity of LASC (Light And Soft Compressible) seed cotton ball, the relationship between the physical properties of LASC seed cotton ball and the resistance coefficient were established by using the dimensional analysis method and the force balance principle, then the theoretical algorithm of LASC seed cotton ball suspension velocity was proposed based on the conventional particle suspension velocity theory. Then, the diameter of LASC seed cotton ball containing a completely cracked single cotton peach were tested in the cotton field, and the minimum diameter of pneumatic cotton conveying pipeline was determined, and the drag coefficient was determined by calculating and analyzing the Reynolds number of pipe flow and around flow. Spherical LASC seed cotton ball with 6 types of densities and 18 types of diameters were prepared by using equal density variable diameter method and the suspension velocities were tested. When the LASC seed cotton balls were just in completely suspended and stabilized at the middle of the glass tube on the test platform, then the suspension speed of the LASC seed cotton balls were calculated according to the relationship between frequency recorded by the frequency modulator and inlet wind speed, and following results were obtained. When a single cotton ball was fully cracked, the value range of the diameter of the seed cotton balls were between 38-54 mm, then the average diameter of the seed cotton ball and the minimum diameter of the cotton conveying pipe were determined to be 50 mm, so the both Reynolds numbers meet the conditions of 500