It has important significance to improve soil quality, reduce the potential risk of eutrophication and greenhouse gas emission through analyzing fertilizer and water coupling mechanism in red soil orchard and implementing precision fertilization.Phosphorus is one of the three essential factors of plant growth and development, and is also an important material guarantee for agricultural production.It is an essential element for crop growth, and limiting factor of the growth of algae.The agricultural non-point source phosphorus has key factor to cause the eutrophication and deteriorate water environment.Comparing with nitrogen and potassium, phosphorus in the soil has the characteristics of strong fixed, low mobility and low utilization rate.The soil strong effect of adsorption to phosphorus is one of the main causes of soil low phosphorus bioavailability.As an adsorption reverse reaction, Desorption process had effect on soil phosphorus speciation, phosphorus absorption of plant, and restricted on transport and environmental effects of phosphorus in the soil.Therefore, the adsorption and desorption of phosphorus directly affected the form, effectiveness, migration and transformation of phosphorus in the soil.So the research of phosphorus is always a hot spot in the field of soil nutrient, and the study on the adsorption and desorption of phosphorus is much concerned.Different types of textures had significant correlation with the effective nutrient content.The different kinds of soil particles had different specific surface, surface adsorbed, different pore size and continuity caused by different article arrangement.These will affect nutrient diffusion in the soil, especially phosphorus.At present, there is little research on the relationship between phosphorus adsorption and desorption characteristics, soil texture and the quantitative relationship between phosphorus diffusion and phosphorus adsorption and desorption.Firstly, combining with the characteristics of red soil orchard and applying soil and groundwater solute transport research results, this paper divided soil phosphorus into precipitated phosphorus and dissolved phosphorus, analyzed adsorption and desorption process of phosphorus and established reaction equation according to the related reference research.Secondly based on international commercial software COMSOL multiphysics, P fertilizer migration simulation model was established in the study area.Soil was divided into two layers, and the permeability of top layer soil was slightly low than below, as shown in Figure 1.Referring the actual fertilization process, liquid phosphorus fertilizer was released for 1 hour.The migration principles of P fertilizer in red soil orchard were analyzed with the time and demonstrated transmission ranges and the concentration distributions of the fertilizer.After 6 days the typical distribution of precipitated phosphorus and dissolved phosphorus were as shown in Figure 2.The results showed that dissolved P fertilizer gradually spread to the surrounding with time.Because of adsorption effect,the concentration of dissolved P fertilizer decreased gradually, finally disappeared.Due to adsorption, the fertilizer concentration of precipitated phosphorus increased, and distribution ranges also expanded with the time.While dissolved adsorption effect, P fertilizer concentrations of precipitated phosphorus decreased slowly.Through forecasting the concentration distributions and spread ranges of fertilizer, the precision fertilization can be processed.