The steam pressure equation is deduced with the momentum theorem while the steam quality equation is deduced with energy balance.The model is solved with nodal analysis and numerical calculation.The property parameters of the steam mixture are calculated with the traditional Beggs-Brill method.The calculation results are compared with the detection on 10 steam injection wells (Qi 40 and Du 80)in Liaohe Oil Field,which indicates that this model works well in calculating the steam properties of steam injection wells.