Nondestructive evaluation of melon quality is in great need of comprehensive study. Soluble solids content (SSC) and firmness are the two indicators of melon internal quality that mostly affect consumer acceptance. To provide guidance for fruit classification, internal quality standards was preliminarily established through sensory test, as: Melon with SSC over 12° Brix, firmness 4–5.5 kgf · cm^-2 were considered as satisfactory class sample; and SSC over 10° Brix, firmness 3.5–6.5 kgf · cm^-2 as average class sample. The near infrared (NIR) nondestructive detection program was set as spectra collected from the stylar-end, Brix expressed by the average SSC of inner and outer mesocarp, each cultivar of melon was detected with its own optimum integration time, and the second derivative algorithm was used to equalize them. Using wavelength selected by genetic algorithms (GA), a robust SSC model of mix-cultivar melon was established, the root mean standard error of cross-validation (RMSECV) was 0.99 and the ratio performance deviation (RPD) nearly reached 3.0, which almost could meet the accuracy requirement of 1.5° Brix. Firmness model of mix-cultivar melon was acceptable but inferior.