Hydrothermal liquefaction (HTL) is an important thermochemical technology which uses hot pressurized water to convert wet biomass or biowaste feedstocks into biocrude oils and other marketable bio-chemicals. However, the widespread commercialization of HTL technology could be challenging due to the corrosion of process core equipment, especially the refining reactors. The presence of hot pressurized water, aggressive catalyst, and organic products can lead to serious corrosion damage and even stress corrosion cracking risks on HTL reactors. Lignocellulosic biomass comprises three primary components: cellulose, hemicellulose, and lignin. These components exhibit distinct behaviors during HTL conversion, leading to variations in the chemical environment and properties of the resulting products. This study aims to compare the corrosion modes and extents of a typical austenitic alloy (UNS R20033) under HTL of three typical biomass model compounds (cellulose, xylan, and alkali lignin) to facilitate the development of corrosion mechanisms in biomass HTL environment.