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 (Da)in the water unsaturated soils increased with increasing soil water content (W) or decreasing soil water suction (S). The relationship between Da and W or S could be described by the power equation of Da=aWb or Da=aS-b. The effect of soil texture on Da value was closely related with moisture condition. Under the same water content, the lighter the soil texture the higher the Da value, and a significant positive correlation of Da value with clay content was observed. On the contrary, at equal water suction, a negative correlation between Da value and clay content was found normally. The porous self-diffusion coefficient (Dp) in water saturated soil was higher 102-103 fold than the Da value of the soil, but there were no differences between the soils. The Da or Dp value increased with the temperature, and every increase of temperature 10℃ within 5℃ to 45℃ caused the Da or Dp 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 coefficient"and "temperature coefficient "advanced in this paper.