Regression isogram was employed to analyze temporal and spatial variation of soil moisture in cornfield mulched with straw and plastic film.The results showed that soil moisture in CK,Treatment SM (straw mulching),and Treatment PM (plastic film mulching) all followed the same trend of going down first and then rising up' with the time in the experimental period of 250 d;and then the trend turned downward again with the depth in profile to 150 cm.The decreasing in soil moisture with the time was parallel to the rising intensity of soil water consumption by corn.The lowest soil water zone occurred much earlier and much closer to the soil surface in CK than in Treatments SM and PM.Treatment PM dropped the most rapidly in soil water content and its lowest soil water zone had a trend of extending downward,whereas Treatment SM had the highest soil moisture content in the lowest soil water zone.The soil moisture of cornfield in CK and the 2 treatments began to increase continuously from the late growth period of corn to the end of the experiment (Jan.4,2003),much more in the upper layer than in the middle layer or bottom layer.It can thus be inferred that regression isogram can be used to reflect the trend and pattern of the temporal and spatial variation of soil moisture and has the characteristics of being simple and time-saving,explicit in graph,vast in information,and easy to analyze.Therefore,it can be used as a good tool for collation and analysis of soil moisture data.