The measurement probe system based on the method of single fame and single exposure imaging (SFSEI) was developed and applied to measure coarse water droplets in wet steam flow behind the last stage of a 330 MW low-pressure (LP) steam turbine.The wetness,diameter and speed of coarse water droplets were measured.The results show that the diameter and wetness of coarse water droplets are greatly influenced by the operating load of steam turbine.The wetness of coarse water droplets is relatively higher in the lower load operation,and it would raise with the increase of the operating load of steam turbine,because of the time delay in temperature changing on the surface of blades.The lacing wires have impacts on the formation of coarse water droplets.Thus,the wetness of coarse water droplets would raise when the steam flow passes by the lacing wires.Moreover,the speed of coarse water droplets is influenced by the flux of main steam flow and the diameter of coarse water droplets.