Abstract: Lots of slack coals are produced in the production of coalbed methane, and the slack coal concentration cannot be continuously metered. A laboratory test was conducted to assess the compensation of flow temperature/flow rate to slack coal concentration, and a method for computing the slack coal concentration in the fluid produced from the coalbed methane well was established according to the principle of mass conservation. Furthermore, a real-time monitoring device suitable for slack coal concentration in the fluid produced from the coalbed methane well was developed. This device can monitor the produced fluid density value through a differential pressure type density sensor, and transmit the value to data terminal in real time, so that the real-time slack coal concentration of produced fluid can be obtained through data conversion. Field application shows that the slack coal concentration monitoring device can realize real-time remote data monitoring, with the accuracy subject to the field requirement, which provide bases for the field control of slack coals and the arrangement of production system.