The hydrodynamic dispersion coefficient is an important parameter for simulating solute transport through soils. KH₂PO₄ solution infiltrated into horizontal columns of five types of soils was tested, and their hydrodynamic dispersion coefficients D_sh(θ) were calculated. results showed that the D_sh(θ) of P was the natural exponential function versus the soil water content θ. The increase of D_sh(θ) with θ was faster when the reaction of P with soil was stronger.