Abstract: Liquid organic hydrogen carriers (LOHCs) offer a feasible route for hydrogen storage and transportation; however, their conventional production generally relies on syngas-derived synthesis or external hydrogenation, resulting in long process chains and elevated costs. Biomass fast pyrolysis provides a more direct pathway by converting lignocellulosic structures into light oxygenated hydrogen precursors (LOHPs), thereby partially bypassing external hydrogenation and streamlining the synthesis route for LOHCs. This review selects LOHPs based on molecular abundance and hydrogen production potential, identifies their primary sources, and systematically assesses the gap between experimental and theoretical yields. It then reviews the effects of feedstock composition, interactions among constituents, pyrolysis conditions, and catalytic regulation on LOHP yields. Derived from biomass C–H–O structures, LOHPs are liquid or aqueous-phase precursors with high hydrogen content for subsequent steam reforming. Among them, glycolaldehyde, acetic acid, and acetol are widely distributed in pyrolysis oils. These compounds possess highly reactive oxygen-containing functional groups and are commonly employed as representative model compounds in bio-oil steam reforming studies. Consequently, they are well suited to serve as representative LOHPs. The three LOHPs are mainly produced from cellulose and hemicellulose; thus, biomass rich in these components provides abundant precursors, yet their actual yields remain substantially below the theoretical limit. Interactions among constituents and pyrolysis conditions are key factors governing LOHP yields. Although extensive studies have examined component interactions, their effects on LOHP formation remain inconclusive. Simultaneous yield enhancement of all three LOHPs is difficult to achieve under a single pyrolysis condition. Higher pyrolysis temperatures and heating rates generally favor glycolaldehyde and acetol formation, whereas acetic acid is more sensitive to residence time. A moderate reduction in feedstock particle size generally favors the formation of all three LOHPs. Additionally, retro-aldol reactions constitute key pathways for the formation of glycolaldehyde and acetol, and Lewis acid sites can effectively promote these reactions. In particular, WO₃ can form surface complexes through interactions between W⁶⁺ sites and the carbonyl and α-/β-hydroxyl groups of sugar molecules, thereby inducing selective C–C bond cleavage and promoting the formation of C2 and C3 compounds while suppressing excessive cracking. Consequently, owing to the structural complexity of biomass, interactions among its constituents, competing reaction pathways, and secondary conversion reactions, the experimental yields of these LOHPs remain far below their theoretical limits. Thus, optimizing pyrolysis conditions and directing production of LOHPs require balancing selective C–C/C–O bond cleavage with the suppression of secondary reactions. Additionally, WO₃-catalyzed C–C cleavage of sugars has mainly been verified in hydrothermal systems, and its applicability to fast pyrolysis remains to be systematically investigated. Although the direct production of LOHPs through biomass fast pyrolysis is expected to shorten the synthesis route for conventional LOHCs and enhance the value-added utilization of biomass resources, systematic studies on the simultaneous quantitative formation and directed regulation of LOHPs remain limited. Future research should integrate feedstock structure analysis, target-molecule formation pathways, and key bond-cleavage chemistry; develop synergistic pyrolysis–catalysis regulation strategies; and establish a directed conversion framework linking molecular mechanisms, process intensification, and engineering applications.