In order to precisely measure the stream turbine humidity at the final stage,the parameter measurement model of steam humidity was designed by backward angle scattering method,and the computing methods of this model was studied.The effects of the various parameters on the scattering light intensity distribution of the drop group were qualitatively analyzed,and the backward direction of 150° was set as the lighting angle and simulation experiments were done.The results show that scattering light intensity is related to the stream humidity parameters.On this basis,the steam humidity under the stable and unstable condition was obtained through inversion and optimization.The study is helpful for measuring the steam humidity by laser scattering method.