Flue-cured tobacco varieties K326 was used as materials in this experiment, and correlation analysis were used to investigate the relationship among nicotine, total N content, protein content and pigment content during bulk curing process. Results showed that chlorophyll content in tender leaves, re-greening leaves, heat-forced maturity leaves and over-green and late-maturing leaves had a large number of conversion at 30–38 ℃ and 42–48 ℃, but carotenoid content in these leaves were all slightly and slowly declined during bulk curing process. During bulk curing process nicotine content in different quality leaves exhibited the maximum conversion at 48–54 ℃, 48–68 ℃, 30–38 ℃, 48–54 ℃; while the maximum conversion of total N content occurred at 48–54 ℃, 30–38 ℃, 42–48 ℃, 38–42 ℃; and the maximum conversion of protein content occurred at 30–42 ℃, 30–38 ℃, 30–38 ℃, 42–48 ℃. Multiple regression analysis of the contents of major nitrogen compounds and pigment content showed that the correlation coefficient(R2 ) in tender leaves were 0.622, 0.545, 0.845; in re-greening leaves were 0.608, 0.721, 0.974; in heat-forced maturity leaves were 0.931, 0.883, 0.966; and in over-green and late-maturing leaves were 0.801, 0.881, 0.981.