Abstract: In order to measure the size of wheat flour particles, the authors firstly separated the flour by utilizing gravitational field-flow fractionation and the samples of the flour were divided into three parts. Furthermore, the flour particles were successfully measured with the digital image processing. The separation effect was assessed using optical microscope and CCD. The results show that the flour particles are mainly distributed in three scopes: 17.0～18.5, 6.7～8.0, 2.0～3.5 μm. This presents a novel method for characterizing the flour particles.