Abstract: The cause of the scale is analyzed，and through the test and on-site investigation，the main cause of scale of the drain pipe is due to the failure of the walerproofing of the top surface of the building. The rainwaler penetrated into the concrete and dissolved Ca( OH)₂. The Ca( OH )₂ concentration in the drain pipe is relatively high，and CaCO₃ scale is formed on the wall of the drain pipe. For drainage pipes that have produced a large amount of scaling，the descaling and descaling trealment methods are not ideal. After analyzing the causes of scaling，the waler from the roof of the building should be removed and the roof should the leveled，and then the roof should be dried and repaired to prevent the scaling of the drain，and to mainlain the waler flow capacity of the drain is to reduce the replacement and cleaning investment and extend the life of the drain.

Key words: drainage piping scale, hazard, precaution