This research was supported by a Scholarshipfrom the Scientific Research Foundation for Returned Overseas Chinese Scholars;Scientific Research Foundation of Nankai University;Science and Technology of Maintain of Ecological System And Adaptability Management on the Interlaced Belt of Northern Grassland and Agriculture and Animal (2007CB106802);Scientific Research Foundation of State Forestry Adminis-trationof the P. R.China ("948"item);"Observation Technological Indraught of Characters of Soil Water and Heat in Arid Area"(2006-4-02);Scientific Research Foundation of Tianjin (07JCYBJC12400 ,07JCYBJC12500)