Near-infrared spectroscopy was used to measure total acidity in ‘shatangju’ (Citrus reticulatablanco). The diffuse reflection spectra of 170 intact samples within 500-2 500 nm were collected.The total acidity in intact samples were measured by titration method.After that,the spectra were de-noised using the orthogonal wavelet functions sym8 (level=3).And then the spectra variables were optimized by successive projections algorithm (SPA) and interval partial least squares (iPLS).Finally,the PLS calibration models of intact samples were established and compared.As a result,wavelet de-noising can produce higher SNR and lower RMSE than that of routine method.Wavelength variables were decreased from 2 001 to 14 by biPLS_SPA,and this can help to make the models more concise and robust.The BPNN model produced RP =0.867 and RMSEP=0.061 6 with 14 variables as inputs.