The structure of nascent pyrolysis and gasification char during lignite pyrolysis and gasification changes due to the product branching which holds the key to unveil these mechanisms, but it is notoriously difficult to find the relationship among the reaction time, structural evolution and gasification reactivity of the nascent char. Here, we investigate the changes in the structure of nascent char during lignite pyrolysis and gasification in the entrained flow reactor under N-2 and CO2, respectively. Subsequently, we determine the selective consumption of small aromatic rings and rapid formation of oxygen-containing functional groups. In the initialization phase of gasification reaction, the condensation polymerization between the aromatic rings in char increases, which might result in the rapid decrease of the ratio of aromatic rings and aromatics with not less than 6 rings. The formation temperature of char is responsible for the char stability and the path of gasification reaction. The sensitivity to temperature of the nascent gasification char decreased in the process of non-isothermal gasification. Simultaneously, gasification kinetic parameters shows that the effect of popplycyclic reaction of benzene rings in nascent pyrolysis char due to the changes of chemical structure, which is more intense than that of structure changes of nascent gasification char.