In order to explore the difference and transformation of soil phosphorus forms under different salt gradients, no-salinized soil was taken from the dry farmland in Pingluo, Ningxia as the research object, and indoor culture experiment was conducted, in which three salt gradients of non-salinization (N), mild salinization (L) and moderate salinization (M) were set up by adding NaCl and Na₂SO₄ in equal amounts. The effects of salt gradient on soil phosphorus forms and enzyme activities were analyzed under two treatments of no phosphorus fertilizer (S) and KH₂PO₄ (P). The results showed that: 1) the higher soil salt content, the lower soil available phosphorus content. 2) Soil organic phosphorus content increased with the extension of culture time without phosphorus fertilizer added. In addition to phosphorus fertilizer added, soil organic phosphorus content decreased with the extension of culture time. Under each salt gradient, soil organic phosphorus content showed M>L>N. 3) After 97 days of culture, inorganic phosphorus reservoirs in the three salinized soils without phosphorus fertilizer added were Ca₁₀-P>Ca₈-P>Fe-P>O-P>Al-P≈Ca₂-P. With the increase of salt content, the contents of Ca₁₀-P and O-P increased, while the contents of Fe-P and Al-P decreased under the treatments of adding phosphate fertilizer. 4) Significant positive correlations were found between soil Al-P and alkaline phosphatase (ALP) activity in the treatments without adding phosphate fertilizer. While under the treatments of adding phosphate fertilizers, significant negative correlations were found between soil Ca₁₀-P and O-P with ALP and phytase (PHY) activities, and significant positive correlations between soil Al-P and Fe-P with ALP and PHY activities (P<0.05). From the perspective of the effect of salt on phosphorus form differences, this study provides a reference for exploring the transformation of soil phosphorus form under different salt gradients.