Analysis of the soil moisture content in topsoil,precipitation,transpiration shows that there are multi-dimensional straight line correlation relations between increase and decrease of topsoil soil moisture content,base period soil moisture content,period precipitation and transpiration,in which the increase of topsoil soil moisture content mainly lie on the height of base period soil moisture content and quantity of precipitation,the decrease of soil moisture content mainly lie on the quantity of transpiration and height of base period soil moisture content.The relative soil moisture content is about 50%~65% in topsoil,which needs 15.9~82.3mm of precipitation or irrigated water.There is a multi-dimensional exponential curve relation between precipitation capacity,base period soil moisture content and precipitation.There is also a exponential curve relation between evaporation capacity and the base period soil moisture content.