Based on the theory of unsat urated soil water dynamics

a three-dimensional axisymmet ric model is set up to simulate soil water movement under gravity subsu rface drip irrigation(SDI).Soil water movement is simulated with the aid of Galerkin finite element method and the model is testified wit h experiments.The result shows that this model can be used to simulate soil water infilt ration process wit h higher accuracy u nder SDI.Wetting pattern and infiltration process are simulated concerning different irrigation technique factors.Under the same irrigation quantity

pressure head and emitter diameters have a minute eff ect on the wetting distribution pattern and so they can be ignored in the process of SDI pipe design

while they have a significant impact on the emitter effluent.During t he SDI pipe design

the emitter diameter and water pressure head can be determined according to the field lengt h and t he water loss of infiltration pipe.Moreover

the lower pressure can be adopted.The pipe depth has conspicuous influence on wetting distribu tion pattern and so its de- sign can be based on the field practical situation.All t he conclusions can provide a theoretical basis for rea- sonable gravity SDI design and operation.