The invention relates to a preparation process for preparing glyoxal based on catalytic oxidation of ethylene glycol. The preparation process comprises four steps: pre-preparation of raw materials, preparation of a catalyst, synthetic reaction and filtration and decolorization. Compared with the prior art, the preparation process has the advantages of high universality and simple operation; on onehand, the precision and efficiency of pretreatment and mixing reaction control of the raw materials, such as the ethylene glycol, and the catalyst can be effectively and greatly improved, and the reliability and stability of connection of material mixing pretreatment and mixing processing procedures are improved; on the other hand, the catalytic activity of the catalyst can be effectively improved, and the comprehensive recovery rate of the catalyst is greatly increased; and loss of the catalyst is prevented, and the phenomenon that a glyoxal product is polluted and has reduced quality due tothe loss of the catalyst is effectively avoided.