The present invention discloses a sludge thickness real-time on-line monitor for a drainage pipeline. The sludge thickness real-time on-line monitor includes a scale frame which is matched with the drainage pipeline, a sensor, a junction box and a data processing device; two ends of the scale frame are fixed to the inner surface of the drainage pipeline; the two end points of the scale frame are located in the same vertical direction; and an titanium alloy frame or hard metal frame is adopted as the scale frame. The monitor of the invention can directly monitor the thickness of sludge in the pipeline online, and at the same time can calculate the height of a liquid level accurately. The sludge thickness real-time on-line monitor has the advantages of simple structure, convenient production and flexible use. The monitor is used for the on-line monitoring of the stacking thickness of urban rainwater, sewage and sludge in pipelines and can provide aid decision making support for pipeline maintenance and periodic dredging through monitoring sludge thickness online.