The invention relates to a method for carbon monoxide gas phase synthesis of oxalate, and mainly solves the problem of low space time yield of oxalate due to the low dispersion of an active component Pd crystal grain and low microcrystal content in catalysts in the prior art. The method is characterized in that carbon monoxide and a nitrite ester raw material contact with a catalyst under coupling reaction conditions; the catalyst comprises 0.03-3wt% of at least one selected from metallic palladium or palladium oxides, 0.01-3wt% of at least one selected from rare earth elements or rare earth element oxides and 94-99.96wt% of an alumina carrier; the average particle size of metal palladium or palladium oxide crystal grains in the catalyst is 3-12nm; and the dispersity of palladium is greater than 20%.