Maturity is a core element of tobacco quality，and obviously, the appropriate harvest maturity plays a very important role in improving tobacco quality. Through our near-infrared measurement and data analysis on different periods of harvest maturity on the baked tobacco leaves，we found that the middle leaves in period of appropriate maturity had total sugar and reducing sugar content of 31.8998% and 24.3905%，respectively，while the tobacco Alkali content was 2.6628% ，nitrogen content was 1.9317% ，chlorine content was 0.24795% ，potassium content was 2.0454%. To sum up，the middle leaves in period of appropriate maturity’s chemical composition was the most coordinated, and they belong to the best quality tobacco.