Biomass resources originally produced by photosynthesis and their biodegradable derivatives such as crop straw, vegetable waste, livestock and poultry manure, etc., can be used as organic fertilizers which have huge potentials in replacing chemical ones. However, it is not clear how large the biomass nitrogen reservoir is in a certain region or country. In order to determine the biomass nitrogen reservoir and its potential to replace chemical fertilizers, we took China as a case, investigated 12 kinds of biomass resources and calculated their nitrogen reservoirs. It was found that the total amount of biomass (dry weight) in China was about 1.527 billion t·a^-1 and the urine of animal (wet weight) was about 878.75 million t·a^-1. The sum of them contained 25.53 million t·a^-1 nitrogen, being 4.12 times that of the amount of agriculture plants actual absorption for synthetic nitrogen fertilizers (6.20 million t·a^-1) in the country in 2018. For biomass nitrogen, the biggest contributor came from the manure and urine of livestock and poultry (54.5%), followed by crop straw (22.9%), vegetable waste (9.4%), vinasse, vinegar and soy sauce lees (2.3%), municipal sludge (2.2%), garden waste (2.1%), urban and rural household garbage (1.8%), orchard waste (1.8%), fishery waste (1.6%), Chinese herbal dreg (0.64%), mushroom stick (0.63%), with slaughterhouse waste being 0.13%. We suggest the government should pay more attention to the utilization of biomass nitrogen by returning waste biological resources to agricultural ecosystem and achieve sustainable agricultural development in the future.