To develop high-yield and high-quality maize varieties and alleviate the supply-demand pressure arising from the difficulty in balancing high yield and high quality， this study evaluated protein， starch， and oil content， three key quality traits， in 588 elite maize inbred lines （across four locations） and 939 landraces （over two consecutive years at a single location） using a near-infrared analyzer. By integrating multi-year and multi-location data， we analyzed phenotypic variation， compared trait differences between the two populations， and examined trait correlations. The results indicate that： （1） Landraces exhibited high genetic diversity， with shannon-wiener index H′ exceeding 2.000 for all three quality traits. Oil content displayed the highest phenotypic variation （CV=8.66%） and starch content showed the lowest （CV=2.46%）. Protein content was significantly higher in landraces from the southwest region than those from the Huanghuai region （P=1.4×10^-8）， whereas starch content was significantly lower （P=0.00164）. （2） Elite inbred lines also exhibited rich diversity with H′ values of 2.075， 2.049， and 1.980 for protein， starch， and oil， respectively. The coefficient of variation for protein and oil content exceeded 10% in certain environments， and both traits generally decreased in content from south to north regions. （3） Landraces possessed significantly higher protein （P=1.08×10^-64） and oil content （P=4.4×10^-136） than elite inbred lines， through starch content did not differ significantly between the populations. （4） Significant correlations （P<0.01） were observed among the three traits： starch content was negatively correlated with both protein and oil content， whereas protein and oil content were positively correlated. （5） We identified four accessions with high starch and protein content， three with high oil and starch， and six with high oil and protein， providing valuable genetic resources for analyzing the synergistic improvement mechanism of yield and quality. Additionally， extreme-quality materials ranking in the top 10 for protein， starch， and oil content， respectively， including widely used core inbred lines such as HZ32， PH4CN， and Su37， were selected. In summary， both landraces and elite inbred lines harbor considerable variation in quality-related traits. This study provides a foundation resource for developing high-quality maize varieties and offers practical insights for quality-oriented breeding breeding.