Abstract: Nitrogen(N) plays a key role in the formation of crop yield and quality. This paper reviews the rational N application which includes rate, time and method, and also includes combinations of manure and straw etc. It points out that the severe N loss in the applied process and after fertilization is the main problem of fertilization in Chinese cropland. Based on the farmer investigation and the rational N rate from the field experiments, the proportion of overuse N of farmers fields occupies about 33% of total investigated fields. However, on the basis of regional scale, comparing with average recommended N rate, the average N rate per sowing area for overuse, rational and insufficient N rate account for 20%, 70% and 10% of the total sowing area, respectively. Generally, the phenomenon of overuse is common, especially in cash crop such as vegetable and fruit tree. We further proposed a method for estimating national N fertilizer demand in this paper. By using three different kinds of estimating method and comparing with actual national total N fertilizer consumption from 1980 to 2010, the actual total N fertilizer consumption is not excessive (27.9106 t N annually from 2006 to 2010) if extensive fertilization; but if with the improved fertilization techniques, the total N fertilizer consumption should be about 19.6106 t N annually from 2006 to 2010. Using five different kinds of predicting method shows that the national rational N demand for 2020, 2030 and 2050 is 21.0106 t N, 21.7106 t N and 23.1106 t N, respectively, if we improve the fertilization technologies. On the contrast, the national rational N demand for 2020, 2030 and 2050 is 30.4106 t N, 31.4106 t N and 334106 t N if we still use extensive fertilization. This paper further analysis the differences among China, the US and the Western Europe on the crop production and N fertilization rate. It also further analysis the importance of manure and carbon application on enhancing soil organic carbon and N pools in Chinese cropland.