Chemical amendment is an effective measure to improve soil water and salt environment under saline alkali stress and alleviate land secondary salinization in arid areas of Northwest China. The water and salt transport characteristics and infiltration model parameters of medium saline-alkali soil at different biochemical fulvic acid (BFA) application rates (0g/kg, 1g/kg, 2g/kg, 4g/kg and 8g/kg) were investigated through the one-dimensional vertical infiltration test. The results showed that after the infiltration, compared with no application of BFA, the cumulative infiltration amount at the BFA application rates of 1g/kg, 2g/kg, 4g/kg and 8g/kg was increased by 1.00%, 4.67%, 7.14% and 3.44%. The soil water infiltration rate was decreased first and then increased with the increase of BFA application, respectively, the average volumetric water content of soil profile was increased by 8.90%, 17.70%, 20.41% and 11.67%, respectively. In addition, at the 0~20cm soil layer, the average desalination rates were 5.29%, 27.04%, 42.77% and 14.74%, respectively. At the same time, the Philip model, Green-Ampt model and algebraic model could well simulate the soil water infiltration regulation at different BFA application rates, and there was a functional relationship between model parameters and BFA application rates. Compared with no application of BFA, the soil infiltration rate S and the soil saturated hydraulic conductivity Ks were decreased, and showed a trend of first decrease and then increase with the increase of the BFA application amount, and the minimum value was obtained at application rate of 4g/kg. The suction Sf at the wetting front and comprehensive shape factor α were increased first and then decreased, and the maximum value was obtained at application rate of 4g/kg. Therefore, the application amount of BFA significantly affected the characteristics of soil water and salt transport, and the application amount of 4g/kg had obvious effects on water conservation and desalination of medium salinealkali soil in Xinjiang.