There are two types of water droplets, fine droplet and coarse water in wet steam flow in LP steam turbine. These droplets form main cause of the efficiency drop in LP turbine and blade erosion. Theoretical and experimental research work has been done on the condensation theory and droplets size distribution. In the paper the progress in the research of this field is reviewed and an integrated probe which is capable of measuring the fine and coarse water as a whole is introduced. Some experimental results are presented.