The invention relates to a new process for producing glyoxal by using a complex silver catalyst to oxidize glycol. The process comprises the following steps: adopting a high-pressure steam-spraying and far-infrared combining heating mode to gasify glycol; uniformly mixing the gasified glycol, steam, preheated filtrated air and circulating air in a tertiary mixer before entering a grid-type oxidation furnace integrated with a feed gas-purifying and refining device and filled with an Ag-P-Se/ceramic catalyst; carrying out a catalytic oxidation reaction; rapidly quenching the reacted gas; sendingthe gas to an absorption tower for repeated absorption; and decoloring the gas to obtain a glyoxal product. The process uses the Ag-P-Se/ceramic catalyst with strong activity and has high glyoxal yield up to 85 percent and small impurity formaldehyde product; a grid-type supporting plate overcomes the defects of easily deformed and crack catalyst bed and decreases the resistance of the bed; and the process integrates the purifying and refining device and the oxidation furnace and adopts the high-pressure steam-spraying and far-infrared combining heating mode to gasify the glycol to save energy and shorten the process flows.