Seriousness of the problems caused by sediment deposits in urban sewer pipe has been widely recognized. Using circulating water tank, scouring tests on the sewer sediment with biological activities were carried out, and the influence of biological activities on erosion characteristics of real in-sewer sediment with different volatile solid (VS) contents under open channel flow by controlling the conditions of dissolved oxygen concentrations and incubation time was also investigated. The results indicate that the biological activities exhibited both positive and negative influences on the erosion law of sewer sediment. It improved the anti-erosion capability by enhancing the binding strength between particles, and the erosion resistance was weakened due to the increase of the porosity of the internal structure of the sediment. Meanwhile, the weak biological activities in the sediment with lower organic content can strengthen the erosion resistance with the incubation time. On the contrary, strong biological activities of sediment with high VS content leaded to the weakening of the erosion resistance. The effect of biological activities on erosion characteristic was also related to the shear force of the flow for the sediment with appropriate VS content.