Abstract: A series of soil profile samples were collected from farmland cultivated for different reclamation and utilization time. The types and contents of potassium minerals, as well as the change patterns in total potassium, slow-release potassium, and available potassium content in various particle groups (coarse sand, fine sand, silt, and clay) of the soils over time were analyzed, and the effects of potassium minerals in different particle groups on soil potassium supply were explored. The results showed that: (1) The soil texture of the Wenrui Plain mainly belongs to clay, with high content of clayey and silt fractions. Its potassium-containing minerals are mainly composed of illite, mica, and feldspar. The average contents of total potassium, slow-release potassium, and available potassium in each particle group decreased in the order of clay＞silt＞fine sand＞coarse sand. (2) The total potassium, slow-release potassium content, and potassium-containing minerals in the soils and various particle sizes gradually decreased with the increase of reclamation time, and the decrease range of total potassium was in the order of 0~20 cm＞20~40 cm＞40~60 cm. (3) The decrease in total potassium and slow-release potassium in the soils with the time of reclamation was mainly related to the decrease in mica mineral content in clay and silt. The impact of mica minerals on total potassium in the soils was significantly greater than that of feldspar, and the impact of potassium-containing minerals in clay particles on total potassium in the soils was significantly greater than that of coarse and fine sand. (4) The high potassium content in the soils of the Wenrui Plain was related to the high content of clay and silt fractions. The contribution of clay and silt fractions to soil slow-release potassium and available potassium was significantly higher than that of fine and coarse sand fractions.