Abstract: In this study, sugar-citric acid reaction systems were applied to study the formation of 3-deoxyglucosone(3-DG) and 5-hydroxymethylfurfural(5-HMF). Fructose/sucrose/glucose-citric acid reaction systems were constructed, the effects of sugar type, pH, temperature, types of metal ions and compounds with different valences of sulfur on the formation of 3-DG and 5-HMF were evaluated. The formation kinetics of 3-DG and 5-HMF were analyzed. Results indicated that the three types of sugar had different effects on the formation of 3-DG and 5-HMF. The amounts of 3-DG and 5-HMF produced in fructose and sucrose reaction systems were much higher than those in glucose reaction system. The amounts of 3-DG and 5-HMF in the fructose-citric acid reaction system increased with the decreasing of pH and the increasing of temperature. Ca²⁺, Mg²⁺ and Al³⁺ promoted the formation of 3-DG and 5-HMF. K⁺ accelerated the formation of 3-DG, but had no significant effect on the formation of 5-HMF(P>0.05). Na₂S₂O₃ and Na₂SO₃ inhibited 3-DG and 5-HMF formation, while Na₂S₂O₅ had no significant effect on 3-DG formation, but it inhibited the formation of 5-HMF(P<0.05). Na₂SO₄ promoted 3-DG and 5-HMF formation. The formation kinetics of 3-DG were in accordance with zero-order kinetics model at 70~90 ^oC while it followed second-order kinetics model at 100 ^oC. The formation of 5-HMF followed zero-order kinetics model at 70~100 ^oC.