In the extraction of crude oil to a series of sections produced a large number of sludge, if not treated, will cause serious harm to the environment. Due to the complexity of its composition, it is extremely difficult to study the physical and chemical processes at its interface, so flocculation mechanism is still at the exploratory stage. According to the sludge treatment process, the common flocculation process Summed up and different the main flocculation mechanism and the advantages and limitations of the analysis, In this paper, it summarized the process of common flocculation process according to the sludge treatment and analyzed advantages and limitations in terms of the different main flocculation mechanism. A popular view on flocculation mechanism is adsorption bridging, network scanning, etc. As for micro-organisms flocculation, the mechanism is extracellular cellulose fibrils, Sticky, capsule, extracellular polymer bridging, electrical neutralization, etc, Finally, the prospect of flocculant is prospected.