With the increasing degree of mechanization coal mining, the coal proportion less than 0.5 mm grade was increased year by year in raw coal in our country, which increase the difficulty of the slurry water treatment. However, the treatment can reduce the concentration of Wash water, realize the closed water circuit. And the economy of water resources the reclaim of coal and the protection of ecological environment can be influenced. And the correct detection of slime water concentration is the basis of all work. At present, the gamma-ray detection method is used to test Coal Slurry water concentration, with which there are a lot of inconvenience. The ultrasonic technology is introduced to detect coal slurry water concentration. The ultrasonic attenuation rule in the slurry water and the factors of affecting the acoustic attenuation are researched. The solutions are brought up. Tests show that ultrasonic detection technology can replace the traditional gamma-ray method and has great practical value.