Abstract: Disclosed are a supported composite oxide catalyst and preparation and use thereof. The catalyst has the general formula: FeMoaSibXcOd, wherein X is a modified metal and is selected from alkali metals or alkaline earth metals; a=0.5-5, b=10-50, c=0.001-0.1, and d is the amount of oxygen element satisfying the chemical valence. The catalyst is prepared with the following method: (i) providing an acidic aqueous solution of a surfactant; (ii) dissolving an iron-containing compound and a complexing agent in the acidic aqueous solution, adding tetra C1-4 alkyl orthosilicate, and performing hydrolysis, crystallization and calcination to obtain a precursor; and (iii) forming a mixed liquid of the precursor, a molybdenum-containing compound and a modifying metal compound, drying same and calcinating the resultant, so as to obtain the supported composite oxide catalyst.