The hydraulic head distribution of seepage field is the basis of seepage discharge and seepage hydraulic gradient calculation. Calculating the hydraulic head distribution of seepage field accurately and effectively is the key link in the calculation of seepage. According to the flow equation of unidimensional steady flow in homogeneous unsaturated soil and the functional relationship between hydraulic conductivity and matric suction

an analytical general formulation of seepage field is obtained with mathematical transformation. In addition

based on the Gardner model

the analytical solution of unidimensional steady flow hydraulic head vertical distribution in unsaturated soil is derived. The general formulation indicates that the unidimensional steady flow hydraulic head vertical distribution is mainly controlled by such three factors as surface water head

depth and rate of flow. Under the condition of unidimensional steady evaporation

the hydraulic head distributions of two typical soils in vertical direction

namely silt and clay

are calculated respectively. The result shows that under the steady evaporation condition

the laws of hydraulic head distribution of silt and clay in vertical direction are similar. With the increase of depth

the characteristic of hydraulic head distribution shows an accelerating degressive tendency from surface to groundwater level. The hydraulic head in clay is higher than that in silt under the same evaporation condition. For the same soil

the faster the evaporation

the higher the hydraulic head. Conversely

the hydraulic head is lower.