On the basis of temperature influences on diffusion transmission factor(f) through influencing water viscosity (η), it was advanced that viscosity correction coefficient (κ) could be described by the equation κ=η₂₅/η_o where η₂₅ and η_x, stand for the water viscosity at 25℃ and x℃,respectively, and the modified Nye model to estimate the diffusion coefficient of phosphate in soil under varying temperature was in the form of D=D₀κfθ/b. By using the adsorption isotherm slope (b) under a lower ratio of solution to soil and lower concentration of phosphate solution, the diffusion coefficient predicted by the model was in agreement with the diffusion coefficient measured, especially at indoor temperature. The ratio of the predicted phosphate diffusion coefficient to the measured phosphate diffusion coefficient in soil under low water tension condition(<105 Pa) was lower than 2 in most cases.