Abstract: Abstract: In order to clarify mechanisms behind the influence of interlayer established by different physical forms of corn straw in saline-alkali soil on soil infiltration characteristics, the indoor simulation experiment method was adopted. A total of 4 treatments of different straw forms buried with the equal thickness of 5 cm at 40-45 cm under topsoil as an interlayer were designed, including no straw interlayer (CK), segmented straw with 5 cm length (SL), straw pellet (SK), and straw powder (SF). The computed tomography (CT) images were used to quantitatively analyze the pore parameters such as porosity and pore size distribution of the straw interlayer and its relationship with the infiltration rate of irrigation water. The results showed that compared to CK, the corn straw interlayer with different physical forms significantly increased the total porosity of the 40-45 cm layer, with SF as the highest, which was significantly higher than that of CK, SL and SK by 29.25, 12.09 and 12.61 percentage points (P < 0.05), but the difference between SL and SK treatments was not significant (P>0.05). The porosity with pore diameter ≤ 1 mm in the SF treatment significantly increased at each stage of irrigation water infiltration (P < 0.05), and increased by 19.18, 17.25 and 9.45, 9.41 percentage points than that of SL and SK before and after infiltration, respectively, which thereby increased the volume of the enclosed gas and resulted in a slower infiltration rate. The porosity with pore diameter > 1 mm in the SL treatment was 1.04 percentage points higher than that of SK before infiltration, but that in the SK treatment was significantly higher than SL after infiltration. This transformation of macropores with pore diameter > 1 mm resulted that the wetting front of SK had taken longer time than SL through the straw layer, while the wetting front had taken less time than SL after passing through straw layer to the bottom of the soil column. Correlation analysis showed that there was a significant positive correlation between the time of wetting front through the straw layer and the total porosity, the porosity of pore diameter ≤ 1 mm before and after the infiltration, but there was a significant negative correlation with the porosity of pore diameter > 1 mm porosity before infiltration (P < 0.01). However, the effect of this macropores weakened after the end of infiltration, the effect of ≤ 1 mm porosity in straw interlayer was still significant, and the effect of pore connectivity on the infiltration rate of irrigation water was observed. In conclusion, different forms of corn straw interlayer affected the infiltration process of irrigation water, and computed tomography (CT) images can be used as a method to quantitatively study the pore structure of straw interlayer and their influence on the infiltration characteristics of irrigation water. This study provides a method for screening and establishing an optimal physical form of straw interlayer combined with salt leaching promoted by irrigation water in saline-alkali soils.