In order to elucidate the basically variable rule of rice grain quality traits in Jiangsu Province, the effect of site and sowing date on grain milling quality, appearance quality, eating quality and nutrient quality was studied in five rice planting regions with five different dominantly cultivated japonica cultivars as material under seven sowing date treatments. The main results showed that the effects of site, sowing date and cultivars on the grain qualities were highly significant, the order of effect on most rice grain qualities was as follows: cultivar> site> sowing date. The change tendency of quality traits varied with site. Grain length, grain width and ratio of grain length and width changed slightly at different latitudes. Amylose content, gel consistency, gelatinization temperature and taste value were higher in the north than in the south while chalkiness rate, chalkiness degree and protein content were higher in the south than in the north. Eating quality showed an increasing trend with increasing latitude. Along with the delayed sowing date, milling quality, amylose content, gelatinization temperature and protein content showed an increasing trend. Grain length and ratio of grain length increased whereas grain width and gel consistency decreased with delaying sowing date. Chalkiness rate and chalkiness degree were significantly different among different sowing dates with little change. And earlier or delayed sowing would result in the degradation of taste value. The response of different traits to the site and sowing date was different. Brown rice rate, grain length, grain width, ratio of grain length and width and milled rice rate were rather stable, but chalkiness rate and chalkiness degree were relatively sensitive to environmental factors. Head milled rice rate, gel consistency, protein content, amylose content, gelatinization temperature and taste value were intermediate between the above two types. The stability of various quatity traits for different cultivars varied with the site and seeding time. Nanjing 46 with the best composited quality characters, was more sensitive to the site and sowing date.