Raman spectroscopy has been applied to characterize the W-O tetrahedron on supported tungsten oxide catalysts. The existence of distorted WO4 has an important influence on its catalytic properties. When Na+ ion is added to WO3/SiO2 catalyst, the distorted WO4 tetrahedron forms, and the selectivity to C-2 hydrocarbons significantly increases. The W-O bond order may be correlated with the selectivity to C-2 hydrocarbons.