Abstract: To elucidate the synergistic regulation mechanism of alkali and alkaline earth metals (AAEMs) and their associated acid radical anions on the three-phase (gas, liquid, and solid) product distribution during cellulose pyrolysis, this study employed cellulose as a model compound. AAEMs of different types (K⁺, Na⁺, Ca²⁺, Mg²⁺) and concentrations (0.25, 1.0, and 2.5 mmol/g cellulose) were introduced via impregnation, and the effects of various acid radical anions (SO₄^2-, CO₃^2-, Cl⁻, HCO₃⁻, CH₃COO⁻, PO₄^3-) on the catalytic behavior of K⁺ were systematically investigated. Pyrolysis experiments were conducted in a fixed-bed reactor at 550 ℃ under N₂ atmosphere. The gas composition was analyzed by GC, bio-oil components by GC/MS (peak area normalization), and biochar by ultimate/proximate analysis and calorific value measurement. The results demonstrate that the type of AAEM determines the product distribution. Alkaline earth metals (Ca²⁺, Mg²⁺) exhibit stronger catalytic activity than alkali metals (K⁺, Na⁺), promoting biochar formation while suppressing bio-oil yield. For gaseous products, alkali metals favor CO generation (up to 68.02 vol.% under K⁺ catalysis), whereas alkaline earth metals preferentially enhance CO₂ production. For liquid products, alkali metals promote the accumulation of sugars (up to 31.79% with KCl), while alkaline earth metals strongly catalyze the enrichment of furans (up to 76.1% with CaCl₂). These differences are attributed to the distinct Lewis acidity and coordination ability of the cations, which affect glycosidic bond cleavage, dehydration, and ring-opening reactions. Furthermore, the acid radical anions finely modulate the catalytic selectivity of K⁺. The biochar yield follows the order: K₃PO₄ > K₂CO₃ > K₂SO₄ > KHCO₃ > KCl ≈ CH₃COOK. Notably, CH₃COOK and K₂CO₃ significantly promote H₂ generation (up to 26.34 vol.%), while PO₄^3- uniquely enhances CO selectivity (up to 64.94 vol.%). In terms of bio-oil composition, K₂CO₃ and KHCO₃ mainly promote the formation of ketones, alcohols, esters, and hydrocarbons (total 65–85%), with furans and acetals being undetectable. In contrast, other potassium salts (K₂SO₄, K₃PO₄, CH₃COOK, and KCl) lead to more complex product distributions: KCl and K₂SO₄ favor sugar formation, whereas K₃PO₄ and CH₃COOK promote carboxylic acids, ketones, and furans. These variations arise from differences in basicity, coordination ability, and thermal stability among the anions, which influence dehydration, decarboxylation, and secondary cracking pathways. Overall, this study reveals the synergistic catalytic roles of AAEMs and their associated anions in cellulose pyrolysis. By rationally matching metal cations and acid radical anions, the product distribution, gas composition, and bio-oil chemical structure can be directionally regulated. The findings provide a solid theoretical basis for the targeted production of value-added chemicals, hydrogen-rich gases, and high-quality biochar from biomass pyrolysis.