Abstract: Abstract: Food processing is designed to meet the supply for better shelf life for food and its materials, where pulsed sudden decompression flashing drying (PSDFD) is a kind of new type, environmental protection and not fried fruit and vegetable drying technology that give better quality to products. In this experiment, drying technology of hot air joint PSDFD was adopted. Moreover, on the basis of calculating moisture diffusion coefficient, with the combination technology of low-field nuclear magnetic resonance (LF-NMR), magnetic resonance imaging system (MRI), differential scanning calorimetry (DSC) and scanning electron microscope (SEM), the effect of different pre-drying temperature on change of water diffusion, water state, glass transition temperature and microstructure was analyzed in the paper. Further analysis of water diffusion characteristic and microstructure under different pre-drying temperature PSDFD was expounded as well. NMR and MRI as a non-destructive, non-invasive, promising technique has been used in detecting the water state, moisture diffusion and movement by the trace of 1H2O proton activities. DSC is another tool to quantify water migration in food and control the shelf life. The correlation between the results of moisture content, water state, water activity (aw) and glass transition temperature (Tg) were also analyzed. In the study, fresh Fuji apple was peeled, pitted and cut into sector slice with 5 mm thickness and then placed evenly on the tray under different temperature of 50℃, 70℃, 90℃ until the water content reached 30%, finally went into PSDFD stage with flashing temperature of 95℃ and vacuum temperature of 70℃. Experiment results showed that, moisture diffusion rate was accelerated along with the pre-drying temperature increasing. As expected, the drying time was effectively reduced by high temperature, and the average drying rate proportion of 50℃, 70℃, 90℃ was 1:1.3:2. High temperature at 90℃ could directly shorten drying time, but reduce nutrition quality greatly. Thus 70℃ was selected as the best pre-drying temperature with its suitable color and crisp taste. Calculated by Fick's second law, the effective moisture diffusion coefficient up with increasing temperature, and ranged from 9.84×10-9 to 7.24×10-8 m2/s. All these explained that higher temperature facilitated moisture migration rate from interior to surface and evaporation rate from surface to air. Moreover, drying effect caused water state changes and moisture with high degree of freedom moved to the moisture with low degree of freedom. Free water existed in plant catheter and vacuole firstly diffused due to its low degree of bondage. Mutual transformation occurred between different states of moisture during PSDFD. Carbohydrate concentration increase and degradation of nutrients in cytoplasm resulted in the proton exchange action, which usually occurred on hydroxyl between water molecules and polysaccharide matrix. MRI showed that water in the fresh samples focused on its center. Then, moisture diffused outward and distributed uniformly in the sample during drying. A trend of decline was shown in brightness of MRI images with the water content decreasing, while the sample presented shrinkage to the center. A significant correlation were obtained from water content and Tg (r>0.90, p<0.01) that moisture decreased leading to glass transition temperature rising. As well, water content strongly effected aw (r>0.93, p<0.01) during PSDFD and water activity reduced with water content declining. In addition, a linear correlation were represented between Tg and aw (R2>0.81) under Origin analysis where Tg decreased with aw increasing. Fresh apple is composed of a large number of swelling cells with compact connection and regular shape. Clear edge structure was showed in the micrograph for it untreated by SEM. Water loss resulted in the changes of microstructure and cell rupture into a cavity. Porous structure was created by vacuum effect under pulsing, which gave product crisp taste. This test could provide the theoretical basis and technical reference for apple slices in PSDFD.