Benefit of shelterbelt and its influence on crop yields in west region of Weibei loess plateau was studied in this paper。The results showed that the shelteibelt was able to weaken wind speed by 22. 2Yo in spring. The best defensive effect place was for from the tree in a distance about 3^"7 times of the tree height. The microlimatic conditions were improved on both sides of windbreak，so that wheat yield in the fields among the shelterbelts was increased by 11%~22 0 o

and the corn by 1.5%-14.4% on protected zone The side effects of windbreak was also disscussed. The reason of reduction of output in belts was mainly that the roots.. of the tree competed soil water with crops and the crowrn produced sunshade.