In this study,the cucumber Jinchun 5 was used as experimental material and the experiment adopted randomized block design.Five nitrogen concentration gradients were set up in 2016 and 2017,respectively,and a critical nitrogen concentration dilution model of aboveground biomass of cucumber was constructed.Based on this model,nitrogen absorption model and nitrogen nutrition index model were constructed,and the suitable appropriate nitrogen application rate was calculated for the cucumbers in the greenhouse.The results showed that the relationship between the critical nitrogen concentration and the maximum biomass in the upper ground of cucumber was in a power exponent relationship with %Nc=4.539 7x-0.06,and the correlation coefficient was R2=0.749 6.The critical nitrogen concentration was established based on the model of greenhouse cucumber nitrogen uptake(Nupt),nitrogen nutrition index(NNI) model,which can be used to determine the index of nitrogen nutrition of greenhouse cucumber under the conditions of this study,the test results show that the 295.7~305.5 kg/hm2 is the best appropriate of nitrogen fertilizer of cucumber.