The concentrations of tetroxide dinitrogen （N₂O₄）and pentoxide dinitrogen（N₂O₅） and nitric acid in N₂O₄-N₂O₅-HNO₃ system are measured by the chemical titration and the nuclear magnetic resonance spectra (NMR)combining titration,respectively. And its results from two methods were compared. The effects of the oxidants,the solvents and the sampling methods on the concentrations of N₂O₄,N₂O₅ analyzed by the chemical titration were also investigated. The results indicate that both the NMR combining titration and titration are in agreement and accurate for the analysis of N₂O₄-N₂O₅-HNO₃ system. N₂O₄ concentrations analyzed by using cerium sulfate as oxidant are more accurate than that of potassium hypermanganate as oxidant. The results of sampling by using ampoule ball are better than that of sampling by using pipette. Comparing with the aqueous solutions of sodium hydroxide as solvent to analyze N₂O₅ concentration,distilled water used as solvent gives the higher accuracy and the better repeatability.