Abstract: The alfalfa-crop rotations can make the yield increase and the quality of crop raise. During the influence of alfalfa,there are several factors including crop kind and alfalfa varieties,continued years of planting alfalfa or crop,tillage methods of alfalfa field,alfalfa-N use efficiency of crop as well as fertilization.On the other hand,the rotations can improve the field ecological environment such as to increase nitrogen,organic matter and waterable aggregate structure in soil,to decline soil density.By obsorbing water amountly and biological desalination,alfalfa can decline the ground water level,improve salinized soil,reduce the runoff of water and soil,it also can decrease the pests and weeds.