In order to establish the stable models,the air and pure water background NIRS models were compared.2 mm,3 mm,5 mm,8 mm and 10 mm optical path length NIR spectra of black tea’s solution on air and pure water background were attained to set up single-optical and multi-optical path length NIR models through using partial least squares (PLS) and principle of permutation and combination.The results of using NIR models to predict unknown samples of black tea were examined by t-test statistical method.The results showed that there was no difference between the NIR models with the same optical path length and different background.There was significant difference (P＜0.05) between models with different optical path lengths on the pure water background.In the multi-optical path length models,the performances of NIR models on air background were better than that of the models on water background.The best NIR model combined 5 mm and 8 mm optical path length,whose predictable accuracy was better than that of single-optical path length models.The NIRS models of air background was better than that of pure water background.