Taking the paddy field converted to tea garden in Mingshan District of Yaan City in Sichuan Province as the study objects, and the continuous extraction and environmental magnetic techniques were used to analyze the changes of iron (Fe) forms and magnetic parameters with tea-planting year. The results showed that all soil pedons (0–110 cm) were in order of reducible iron (Red-Fe) > oxidizable iron (Oxi-Fe) > acid-soluble iron (Acid-Fe). Acid-Fe and Oxi-Fe in 0–10 cm and 10–20 cm layers increased significantly when paddy field converted to tea garden and with tea-planting year, while Red-Fe decreased in all soil pedons. Three years after paddy field converted to tea garden, soil magnetic susceptibility (MS), saturated isothermal remanence (SIRM) and soft remanence (IRMs) increased but hard remanence (IRMh) decreased. However, with the increase of tea-planting years, all soil magnetic parameters decreased, and ferromagnetic minerals dominated the change of soil magnetic characteristics. After paddy field was converted to tea garden, soil was gradually acidified and organic matter was accumulated, which made ferromagnetic minerals unstable, and further led to the transformation of Red-Fe into acid-Fe and Oxi-Fe, while the crystallinity of some iron oxides increased with the increase tea-planting year.