Vortex flowmeter is mainly used for the flow measurement of industrial pipeline medium fluids, such as gas, liquid, steam and other media. There are special phenomena and problems in the process of measurement. One of the key problems is that the vapor density value deviates too much from the design value, which brings significant measurement errors to the measurement results. At present, the density measurement instrument with mature technology has not been successfully applied, which brings certain difficulties to the steam flow measurement.