To determine the effect of different agents on the dynamic characteristics of floc structures, ferric chloride (FC) and anionic polyacrylamide (APAM) were dosed as coagulant and flocculant, respectively, to flocculate the coal slime water. Particle vision and measurement (PVM) was employed to monitor the flocculation process in situ. The results showed that the floc could grow to a size of approximately 1 mm only under conditions of 100 mg/L FC and 50 mg/L APAM. The coagulant dosage influenced either the aggregation of the slime particles or the conformation of the flocculant. If the coagulants were insufficient or excessive, the flocculant conformations were stretch chains and resembled unable to bridging the slime particles as shown in the captured images. The variation of the relative backscatter index (RBI) during the process indicated that the required residence time for flocculation was proportional to the ratio of particle size at the end of flocculation to that at the beginning of the process. It can be concluded that PVM is an effective instrument that can obtain useful dynamic information of the flocculation process by combining real-time images and the RBI. • Practitioner Points• The coagulant concentration affects the conformation of the flocculant. • The required retention time is depended on the max size that flocs can reach. • PVM is a powerful instrument for studying dynamic flocculation process in situ. • Key wordsanionic polyacrylamide; coal slime water; dynamic process; flocculation; particle vision and measurement