0.910。A measuring system for soluble solids content (SSC) of watermelon was developed based on near-infrared transmittance technique. The system mainly consists of an available spectrometer, optic fiber transmittance accessories, data sampling card and light source. Prediction test for SSC of 50 ‘Qilin’ watermelons were carried out by the system. The calibration models between the spectra (the original spectra, its first derivative, and its second derivative) and SSC were established using partial least square and principle component regression methods. The results showed that the second derivative spectra with partial least square method provided the best prediction of the SSC of watermelons with the correlation coefficient of 0. 951, the root mean square error of calibration of 0.347 and the root mean square error of prediction of 0.302. The correlation coefficient between predicted and measured values is 0.910.