Thermal dissolutions (TD) of Indonesian lignite at different temperatures and by catalysis of Mo-Ni or not were carried out to analyze the effects of Mo-Ni on the constituent ingredient and composition distribution of soluble portion. Formation mechanism of the soluble portion was also investigated. The results of GC-MS analysis show that a small amount of esters with long straight chains initially formed caused by physical thermal dissolutions. With the increase of temperature, the esters increased, but more esters were comprised of smaller molecular. The further increase of the temperature, relative content of the esters drastically reduced, aromatic hydrocarbons and phenols became the main constituent ingredient of the soluble portion. Under the action of Mo-Ni, beta scission and dehydrogenation lead to the formation of short-chain methyl alkanoate, n-alkanes and 1-alkenes from long-chain methyl alkanoate. The short-chain methyl alkanoate further produce n-alkanes directly or indirectly by a series of reactions, such as catalytic cracking, decarboxylation, dehydroxylation, hydrogenation and deoxidation. The n-alkanes and 1-alkenes transform into low-carbon olefins caused by oligomeric activity and acidity of Mo-Ni, and then the olefins are polymerized to benzene rings. The rings are methylated, nucleophilic substituted, and polymerized to produce aromatic hydrocarbons and phenols.