Abstract: The characteristics of algal source foulants could affect the membrane fouling during the treatment of algae-rich water by microfiltration. Filtration experiments were carried out with algal cells, algogenic organic matter (AOM) and algae suspension at different growth phases to study the influence of algal source foulants characteristics on membrane fouling and its mechanisms. The UMFI method was used to analyze the fouling degree of algae cells, AOM and algae suspension at different growth stages. In particular, the changes in their fouling contribution ratios at different growth phases were further elucidated based on the criteria importance through intercriteria correlation. Meanwhile, the mixed fouling blocking model was used to analyze the main fouling blocking types at different filtration stages of algae suspension at different growth stages. The results showed that the membrane fouling caused by algae cells and AOM in the exponential phase was the lowest compared with the other two growth phases. Notably, the contribution of AOM and algae cells to membrane fouling varied with the growth phase during the treatment of algae-rich water by microfiltration. The objective weight of fouling caused by AOM decreased with the prolongation of growth phase, and the declining phase reduced to 10.2%. Meanwhile, the objective weight of algae cells increased with the prolongation of growth phase, and the exponential phase was only 28.3%. In the filtration process of algae suspension at different growth phase, there were all two stages of fouling mechanisms, and the latter stage was cake formation. These results not only elucidated how the changes in the characteristics of the algae suspension affected characteristics on the membrane fouling and disclosed its mechanism during the microfiltration treatment of algae-rich laden water by microfiltration, but also provided theoretical research guidance for the development of membrane anti-fouling improvement technologies.