Determining reasonable nitrogen (N) fertilizer rate is the key point for getting higher target yield, maintaining soil N fertility and reducing environmental pollution. Since N fertilizer invention and application a century ago, although it had been carried out more than hundred of years’ researches, people didn’t find the satisfied methods that could determine the reasonable N application rate on the field scale. Based on the previous concept and method of theoretical N rate (TNR) and on the conditions of considering other sources of nitrogen inputs, this paper further deduce the calculation of TNR according to the N requirement per hundred kilograms (kg) of grain. The results showed that, after determining the N requirement per hundred kg of grain (N₁₀₀), the TNR (N_fert, N kg hm^-2) is the only function of target yield (Y, kg hm^-2) as: N_fert ≈ Y/100×N₁₀₀. After integrating the results from all kinds of literatures, the N requirement per hundred kilograms of wheat, maize and rice was 2.8, 2.3 and 2.4 kg, respectively, under current production conditions and yield levels. Comparing the TNR with economic optimum N rate (EONR) from a large number of field experiments’ results on the literatures, in most case, the two rates are very close in other regions of China except for the northeast China. The TNR of wheat, maize and rice in the northeast region is much higher than the regional N recommended rate (RNRR). The main reason is that the soil N mineralization is greater than immobilization during growth period, which means the crops utilizing part of soil mineralized N and soil organic N is depleted. Combining with the TNR, this paper also analyzed the scientific basis, recommendation results and applicability of other N recommendation methods established in recent years in China in details. The paper recognized that to adjust the excessive and deficient N application rates to the reasonable scope is the urgent task nowadays and in the future, and the TNR could meet this actual demand by maintaining high and stable target yield, soil N balance and low environmental risk. It is very convenient for extension technicians and farmers to determine the reasonable N application rate according to the target yield of their own field.