Abstract: In order to provide theoretical basis for optimization of curing process，the yellowing and browning characteristics of tobacco leaves were studied during curing process. Using middle leaves of K326 cultivar as test material，the changes of yellowing degree，browning degree，starch，protein and dry matter in tobacco leaves with different yellowing temperature were studied. Results showed that the yellowing speed of tobacco leaves increased with the temperature increasing，however，the browning speed of tobacco leaves also increased. The degradation of starch and dry matter of tobacco leaves accelerated with yellowing temperature increasing，protein degradation slowed down，the level of starch and dry matter degradation of the same yellowing degree increased with the temperature increasing，and the level of protein degradation was low. The starch content，protein content and dry matter content were not significantly different in the process of browning，the starch degradation degree was 82%-90%，the protein degradation degree was about 45%-60%，and the degradation degree of dry matter was about 15%-25%，when tobacco leaves turned brown completely.