The invention relates to a method of catalytically synthesizing ethyl methyl carbonate by a calcium magnesium and aluminum composite oxide. The ethyl methyl carbonate is synthesized under a catalytic action of the calcium magnesium and aluminum composite oxide by taking dimethyl carbonate and diethyl carbonate as raw materials. The method is characterized in that the calcium magnesium and aluminum composite oxide is a product obtained by roasting calcium magnesium and aluminum hydrotalcite for 2-8 hours at 400-600 DEG C; the structural formula of the calcium magnesium and aluminum hydrotalcite is Ca<2+>xMg<2+>yAl<3+>1-x-y(OH)2(CO3<2->)(1-x-y)/2.mH2O, wherein (x+y) is greater than or equal to 0.5 but less than or equal to 0.8; x/y is greater than or equal to 0.25 but less than or equal to 4; m which is the number of crystal water is greater than or equal to 1 but less than or equal to 8. The method provided by the invention has the advantages that the catalyst is simple in preparation process and low in cost, the product is high in yield, and the catalyst is easy to separate and has a good performance for repeated use.