Low molecular weight compounds (LMWCs) account for 10-23% of total coal mass. However, their role in coal's spontaneous combustion has not been well understood. In this paper, we first experimentally tested the effects of LMWCs on coal's oxygen consumption as well as heat release and transfer, and analyzed the components of LMWCs in coal, then we measured the oxidation characteristics of main active groups of LMWCs using model compounds method and last presented the mechanisms of LMWCs affecting coal spontaneous combustion. Raw coal with low metamorphic grade had greater oxygen consumption rate and the heat release intensity than the extracted residual coal, while the extracted residual coal of anthracite coal at the higher temperature had higher oxygen consumption rate and the heat release intensity than the raw coal. LMWCs could increase coal's thermal conductivity, lower coal's specific heat capacity, and shorten coal's self-igniting period. Extraction of LMWCs could increase total pore volume and specific surface area of low rank coals. The extracted LMWCs had far greater, even one hundred more times higher, oxygen consumption rates than raw coal. Taken together, LMWCs could significantly promote the spontaneous combustion of low rank coal. Addition of substances that could dissolve LMWCs or inhibit their oxidation during water or cement injecting can significantly prevent spontaneous combustion of LMWCs-rich coal mines.