Under careful control of the molar ratio of V2O5 to N2H4, pure single phase WxV1_xO2 could be obtained by the doping of tungsten in VO2 lattice. Fig. 4 showed the XRD patterns for samples with different nominal doping content of tungsten which referred to the amount of tungsten contained in the recipe. In solid state reaction, the variation of the content for different elements mainly depends on its volatility in high temperature. It is very different for solution reaction case. In hydrothermal condition, volatility is negligible. The variation of the final content mainly depends on the solubility for different chemicals. To determine the final doping amount of tungsten, XRF technology was used and the results were listed in Table 1. Measurements indicated that the real contents of tungsten in final products were higher than its corresponding nominal contents. These results also revealed that some vanadium remained in the solution after hydrothermal treatment.