Abstract: This paper studied the effectiveness of organic nitrogen in the soil of solar greenhouse, and provided a theoretical basis for scientific fertilization. In a tomato pot experiment, biological depletion method was used to study the nitrogen availability of different kinds of organic manure (four chicken, two pig and three cattle manure samples). The results demonstrated that chicken manure, pig manure and cattle manure could significantly increase tomato biomass and the uptake of nitrogen. The tomato aboveground biomasses increased by 28.63%, 7.75% and 12.28% respectively, and the nitrogen absorption amount increased by 14.06%, 6.61% and 7.48% respectively. The nitrogen utilization rate and the equivalent mineral nitrogen rate of chicken manure was 37.79% and 40.73% respectively, significantly higher than those of pig manure (9.12% and 10.93%) and cattle manure (13.36% and 15.71%). Though the characteristics of different organic manure were different, the nitrogen availability of organic manure was obvious.