In the present study, an orthogonal array design was adopted to investigate effects of operational parameters including aeration intensity, membrane flux, suction time and non-suction time on sludge accumulation on membrane surfaces respectively at a high SS concentration of 10g 1-l and a low SS concentration of 1g I-1 in a submerged membrane bioreactor. Average transmembmne pressure (TMP) increase rate over the operation time was used to evaluate sludge accumulation. Among the four factors, membrane flux was found to influence Th4P the most obviously. The effect of aeration intensity became significant only at a high SS concentration of 10g I-1TMP increased with suction time and decreased with non-suction time. There was a critical membrane flu over which sludge particles were deposited, and accordingly, ThW increased sharply. Two zones, predicting whether sludge particles are deposited or not, could be comprehensively determined by the critical flux, correspondent aeration intensity and SS concentration. For long-term stable operation, it is suggested that a membrane bioreactor be operated in the zone with prediction of no obvious sludge deposit on membrane surfaces.