Self-diffusion coefficients of phosphate in four soils of different texture at varying water content and temperature were measured by the methods of diffusion half-cells and diffusion tube using ³²P-labelled KH₂PO₄ solution.The results showed that the apparent self-diffusion coefficient (D_a) in the water unsaturated soils increased with increasing soil water content (W) or decreasing soil water suction (S).The relationship between D_a and W or S could be described by the power equation of D_a=aW^b or D_a=aS^-b.The effect of soil texture on D_a value was closely related with moisture condition.Under the same water content,the lighter the soil texture the higher the D_a value,and a significant positive correlation of D_a value with clay content was observed.On the contrary,at equal water suction,a negative correlation between DQ value and clay content was found normally.The porous self-diffu-sion coefficient (D_p) in water saturated soil was higher 10²10³ fold than the D_a value of the soil,but there were no differences between the soils.The D_a or D_p value increased with the temperature,and every increase of temperature 10℃ within 5℃ to 45℃ caused the D" or D_p value to increase by about 10-50%,with an average of 30% or so.Moreover,nonlinear multiple regression analyses were used to investigate the relation between the interaction of soil moisture with temperature and the self-diffusion coefficient of phosphate in soil.The analytical results indicated that the interaction influenced the diffusion of phosphate clearly,and the influencing extent could be defined by the concepts of "water coeffeient" and "temnerature coefficient" advanced in this naner.