The color rendering quality of RGB-LED light source is mainly evaluated by color rendering index, gamut, color discrimination ability of observer and object color saturation. However, the possible chromaticity mismatch range that all spectral reflectances metameric to one surface under standard illuminant D65 would form under a RGB-LED light source with correlated color temperature 6500 K has not been thoroughly studied. First, the peak wavelengths of blue, green, and red LED light source were changed respectively, and the simulated RGB-LED light source spectrum was generated by Gaussian distribution function. Then, chromaticity mismatch areas under RGB-LED light source formed by all spectral reflectances metameric to 12 Munsell surfaces under standard illuminant D65 were calculated. Finally, the data of five real RGB-LED light sources were analyzed. The results show that the chromaticity mismatch region corresponding to the Munsell color card was negatively correlated with the general color rendering index of RGB-LED light source, that is, the larger the general color rendering index of RGB-LED light source, the smaller the chromaticity mismatch region corresponding to the Munsell color card.