Abstract: Potato, apple and carrot were chosen to study the effect of hot-air drying on their microstructure. By using the paraffin technology, the micro-imaging technology and the image processing technology, the microstructure images under different moisture content during drying were obtained, and the effects of hot-air drying on the parameters, in terms of cell area, cell perimeter, cell equivalent diameter and cell roundness were analyzed from the cell parameters distribution curves under different moisture content. Fitting equations were built to describe the positive correlation between the cell parameter ratios and the moisture ratio during the hot-air drying. The results indicated that the cell changing with moisture content during drying could be predicted by the fitting equations. This study provided a theoretical basis for the quality control and the mathematical model of fruits and vegetables during hot-air drying.