Abstract: The pore structure of the soil is an important factor affecting soil water retention and infiltration properties. Diatomite with porous character can be used to regulate the water retention and infiltration performance of soil, however, the research on the influence of pore structure and surface property of diatomite is not enough, and the water retention and infiltration performance of diatomite have not been studied systematically. Alkali dissolution can regulate the pore structure and surface property of diatomite. In order to improve the basic research on the application of diatomite to regulate soil water retention and infiltration performance, Linjiang diatomite was used as the raw material to prepare alkali dissolution diatomite under different alkali dissolution temperatures, which based on the principle that diatomite's main ingredient is amorphous SiO₂, and the amorphous SiO₂ can react with strong alkali to form sodium silicate at a certain temperature and can be removed by filtration. The microstructure, pore structure and surface functional groups of Linjiang diatomite and alkali dissolution diatomite were characterized by SEM, the low temperature nitrogen adsorption method and FITR. The water retention and permeability of diatomite were quantified by diatomite permeability measurement method and activated carbon water capacity measurement method. The results show that the water retention and permeability of diatomite are affected by the pore structure and surface properties of diatomite. The specific surface area of diatomite increases with the increase of alkali dissolution temperature, which changes the surface hydroxyl group, resulting in the increase of permeability and water capacity of diatomite with the increase of alkali dissolution temperature. Under the conditions of diatomite dosage 50 g, NaOH dosage 10 g, ultrapure water dosage 200 mL, alkali dissolving temperature 90 °C and alkali dissolution time 30 min, the alkali dissolving effect of diatomite is the best, and the permeability of diatomite reaches 0.1507 darcy, which is 14.35 times that of untreated diatomite. The water capacity of diatomite reaches 290.76 %, which is 1.95 times that of untreated diatomite. The specific surface area of diatomite increases from 6.487 m²/g to 9.904 m²/g.