Abstract: In order to monitor the density and distribution of water-drop at the end stage of the steam turbine, the off-axis angular scattering method was proposed to measure the parameters of wet steam. In this way, it not only guides economic operation of the turbine but also guarantee water allowance of the boiler. At the same time, it can reduce the influence of wet steam on the turbine. Based on the structure and parameters of mock cylinder, a mathematic model was built. This mathematic model can find whether the middle radius of quantity, the density of number and the distribution of magnitude in water-drop have impact on the scattering ratio. The wet steam was measured under different conditions. The analysis result was similar to the experimental result. The experimental results proved the off-axis angular scattering method is feasible for measuring wet steam parameters. This research is helpful for monitoring the parameters of wet steam and other particles.