Abstract: The agriculture development of semi arid area in Loess Plateau depends on the natural precipitation completely. But the low total precipitation, the large variance and the unbalanced distribution of natural rainfal make the water supplying and requiring of crop growth be unmatched. The output of crops can be increased by making use of rainfall harvesting project to collect water in abundant rain period, store it in cellars, balance it from time and space, and then replenish proper water to crops in their key period of growth. So the rainfall harvesting agriculture is promoted greatly in the regions of Loess Plateau. The precipitation in this area provides condition to the development of rainfall harvesting agriculture. But during the procession of practicing rainfall harvesting, it appears that cellars were built blindly in some unfitted water collecting area. Rainfall harvesting depends on not only the precipitation but also landform, composition matters of earth surface, and land use etc.. Having analyzed the basic property of landform, the effect of landform to runoff (including effects of slope, length and direction of grade), and the situation of land use at present, the paper partitions different types of water harvesting regions according to the principles of integration, dominant factors, alikeness and otherness, and benefiting for production. It also provides a index system to judge the fitness for water harvesting by landform types, surface curving density, cracking percent of land surface, slope, relative superelevation, makeup of land surface, situation of grade, precipitation, cultivating coefficient, vegetation and so on.Water harvesting area types in the studied area include the most proper region, proper region, inferior region and unfitting region. Different types reflect the differences of run off producing ability in different regions and the proper extent for water farvesting. It can provide theoretical and practical direction for the definition of effective areas of rain harvesting, the scale of engineering, and the distribution of rain harvesting project. It can also help different regions to develop their own rain harvesting agriculture according to different conditions, and avoid unnecessary loss.

Key words: rain harvesting agriculture, semi arid area of Loess Plateau, regional types of rain havesting