Lignocellulosic biomass is the most abundant renewable carbon resource on the planet, which has the potential to replace oil to produce clean fuels and chemicals. At present, the efficient utilization of lignin components is difficult, which is the key to realizing the utilization of all components of biomass. To achieve the high-value utilization of lignocellulosic components, this review investigates the separation mechanism based on the "lignin-first" strategy, compiles the research progress of reductive catalytic fractionation, and explores the factors of yield and selectivity of phenolic monomers, degree of delignification and retention of carbohydrate pulp, analyzed the influence of biomass feedstock, solvent, acid and base additives, catalyst, and reactors on the " lignin-first" strategy. In addition, this review also proposes new design ideas for catalysts and reactors and the research direction of reductive catalytic fractionation. The analysis shows that the yield of phenolic monomers decreases in the order of hardwood→herbaceous crop→softwood. The alcohol-water two-phase system is favorable for the extraction and dissolution of lignin and hemicellulose as well as the retention of cellulose structure. The addition of acid not only improves the degree of delignification and monomer yield but also promotes the hydrolysis of hemicellulose. The semi/full flow reactor effectively avoids the separation of catalysts and carbohydrate pulp.