In order to monitor the diameter change of starch granules in physical or chemical process on line,the influences of the starch slurry concentration,stirring rate and medium on the distribution of the granule diameter were investigated by means of FBRM.Moreover,the granule diameter distribution curves of different starches and the granule diameters of the same starch measured by different methods were analyzed.The results show that（1） with the increase of starch slurry concentration,the granule diameter measured by FBRM first increases and then decreases,and it reaches its maximum at a slurry concentration of 1%;（2） the stirring rate slightly affects the measurement of the granule diameter;（3） the granule diameter distribution becomes stable when ethanol and isopropanol with a concentration of lower than 50%,or glycerol with a concentration of higher than 75%,is used as the medium;（4） the distribution curves of the granule diameter vary with the starch type;and（5） even for the same starch granule,the measured diameter is inconstant due to different measurement methods.