The impact of using visible/near infrared reflection and diffuse transmission spectra to detect the soluble solids content of Gannan navel oranges was studied. Vis/NIR reflection and diffuse transmission spectra of 196 Gannan navel orange samples were acquired by using a QualitySpec spectrometer in the wavelength range of 350~1 800 nm. Regarding these 196 samples, 147 samples were used as the calibration set to build calibration model, and balance 49 samples were used as the prediction set to validate model.Then a variety of pretreatment methods combined with partial least squares regression was used to develop the prediction models of SSC of navel oranges corresponding to a single spectrum and an average of three times spectra for Vis/NIR reflection and diffuse transmission spectra respectively. It is found that the diffuse transmission spectra prediction model is much better than the models of a single spectrum and an average of three times spectra. The partial least squares regression prediction model of Gannan navel orange based on the average of three times diffuse transmission spectra combined with multiplicative scattering correction pretreatment method performs the best, and the correlation coefficient and the root mean square errors in the calibration and prediction model are 0.980, 0.230°Brix and 0.949, 0.374°Brix respectively. So the average of multiple diffuse transmission spectra is more suitable for detecting the SSC of navel oranges.