For improving aviation biofuel in quantity and quality, main precursor compounds have been investigated on the hydrotreating mechanism, including triglycerides by lipid extraction, fatty acid methyl/ethyl esters by transesterification, and fatty acids by hydrothermal liquefaction. Hydrotreating tests have been conducted on the effects of temperature, pressure, catalyst loading, and reaction time at molecular level. Fatty acid methyl/ethyl esters are the most desirable hydrotreating compounds for their highest biofuel yield and mildest upgrading conditions(≥290 °C, ≥10% catalyst loading). At the proper conditions of 290 °C and 30% catalyst loading, methyl stearate can yield 61.6% biofuel with 100% selectivity to alkanes. Fatty acids are the most difficult compounds to upgrade and should be hydrotreated above 310 °C and at least 30% catalyst loading, otherwise there are unconverted fatty acids, fatty aldehydes and fatty alcohols in the products. C30+ heavy esters are commonly found in the undesirable products and suppose to be derived from esterification of fatty acids and fatty alcohols under low temperature. Enhancing carbon number and unsaturation of the precursors promote the generation of olefins and oxygenates.