Blue tungsten oxide (BTO) is an important raw material for production of tungsten powder. It doesn’t have a single tungsten oxide valence, and it is composed of W5+ and W6+ valences. With the reduction of oxygen content, valence of tungsten decreased gradually. Slight hydrogen ion etching, vacuum annealing and industrial hydrogen reduction treatment are processes of loss oxygen, but also change the process of tungsten from high valence to low valence, blue tungsten oxide can be two to three valence composition. Valence can be characterized by X-ray photoelectron spectrum.