Abstract: The effect of water and nitrogen fertilizer on crop production in farmland in loess plateau was studied by the field experiments conducted in Yongshou county and Yangling, Shaanxi province on the basis of analysis of many others experimental results It was showed that the result of simulated experiments didn't coincide with the field situation The results of field experiments showed that fertilizer contributed more to crop yield than irrigation water At the present water resources situation, the main way to increase crop yield in most farmland of loess plateau was increasing nutrients supply Enhancing the storage of rainfall during summer fallow period and raising soil water content before sowing were important factors to obtain high winter wheat yield The key irrigation time was related to soil water content before sowing, precipitation during crop growing and the precipitation distribution etc Both of winter wheat and summer corn has still great potential to increase yield