The present invention provides a complex oxide catalyst whose general formula is Mo12VaCubWcXdYeOf/Z. reducing agent needs to be added into the catalyst during the preparation process of the active component of the catalyst and (or) molding process of the catalyst. Specifically, X is at least one selected from a group consisting of Nb, Sb, Sr, Ba and Te; Y is at least one selected from a group consisting of La, Ce, Nd, Sm and Cs; “a” is ranging from 2 to 8; “b” is ranging from 1 to 6; “c” is ranging from 0.5 to 5; “d” is ranging from 0.01 to 4; “e” is ranging from 0.01 to 4; f is determined by the oxidation state of the component element; Z is silicon powder; the reducing agent is C2˜C6 diol or polyol.