Abstract: Concentration of process water is an essential indicator for evaluation of grade of closed process water circuit of a coal preparation plant, and accurate and rapid measurement of process water concentration is therefore of vital importance for coal preparation operations. In order to provide an effective instruction for the measurement of concentration of the water, the paper presents a detailed introduction, based on the interpretation of the concept of concentration of process water, to four measuring methods commonly applied currently in coal preparation plants, including the two methods as specified in the industry standards MT/T 808—1999《Coal Preparation Plant Technical Control》 and MT/T 805—1999《Determination on the SS of Water in Coal Mines》, and another two rapid measuring methods using respectively concentration pot and visible spectrophotometer. Then a detailed account is made on the measuring procedures of each method and the points requiring attention in operation. Result of analysis shows that for the evaluation of grade of process water of closed circuit, the following two standard methods are recommended; and for in-plant rapid determination: measuring high-density water with concentration pot and low-density water with visible spectrophotometer.