The acyloin mixture which mostly consists of C5 acyloin was synthesized from acetaldehyde and propional by cross-condensation under the catalysis of 3-ethyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium bromine.2,3-Pentanedione was prepared through oxiding the mixture indirectly by hydrogenperoxide and separating.The optimized cross-condensation reaction conditions: m（acetaldehyde）：m（propional）: m(catalyst)：m(sodium carbonate)=110：90:2:1；reaction temperature was 120~130℃；the pressure was 1Mpa.the conversions of acetaldehyde and propional were 94% and 95% respectively, The yields of C5 acyloin was 48.8%, the total condensation products amount to 90%.In the presence of concentrated sulfuric acid, acyloin mixture were oxidized by 30%H2O2/ FeSO4·7H2O, m（FeSO4·7H2O）：m（sulfuric acid）：m（water）：m（acyloin）：m（30%H2O2）=11：2：4：2：3, the yield of 2,3-pentanedione relativing to the gross weight of acyloin was 45.5%，the total yields of vic-diketones amount to 84%. 2,3-Pentanedione、butanedione and 3,4-hexanedione can be obtained with purities more than 98% by atmospheric distillation, the iron salt could be reused without obviously decrease of the yields of vic-diketones.The method did not use organic solvent and used H2O2 as oxidant indirectly.It was a green process.