Abstract: Langmuir, Freundlich and its extension equations were adopted to study the soil phosphorus adsorption and desorption characteristics in calcareous fluvo-aquic soil of long-term fertilization experiment. Results indicated that double-surface Langmuir equation and all forms of Freundlich equation could well describe phosphorus adsorbed by soil. Organic manure application could remarkably decrease phosphorus adsorption，which was shown by the decrease of Qm and K values in soil with organic manure addition for a long time. Phosphorus adsorbed by soil with organic manure addition was more easily released than by the soil with only mineral fertilizer application(phosphorus desorption rate was 20% and 15% for these two treatments, respectively). Qm value and K value were increased by potassium addition treatment, indicating that potassium addition promoted phosphorus transformation to more steady forms. This negative effect was evidently corrected by combined use of organic manure and mineral potassium fertilizer.