According to the geological and geomorphical characters

this paperexpounds and analyses the forms

types and causes of soil and water lossof Zhengning county in Gansu province in detail. It thinks that themain forms of soil and water loss in this county are hydraulic and gravi-tational erosions

hydraulic erosion is the leading one.The types of erosionrelates to the angle of hill slope

vegetation density

erosion modulus

strength and the sand discharge carried by water current keeping increasingfrom east to west in this county

the modulus of erosion increases fromless than 500t/km2·y in the east forest area to 600t/km2·y in the west.Based on above analysing

the authors deduce that the causes of soil andwater loss are the special landform with the deep cut gullies

the strati-graphic structure with soft rocks accompanied with hard rocks

the con-centrated rainfall

the active new tectonic movement and unreasonableexploring and utilizing by mankind

etc.