In this study, the variation rule of biological activity of activated sludge in organic matter biodegradation, nitrification and denitrification process in SBR system was investigated by determining INT-ETS activity of various influent nitrogen and organic shock loading. The experimental results showed that: INT-ETS activity could provide a good indication of the ongoing biological reactions of SBR system; Biological activity of organic matter biodegradation, nitrification and denitrification process in SBR system reduced orderly, observably, INT-ETS activity reduced from 232.59mg/(g·h) to 190.65mg/(g·h) and finally to 113.88 mg/(g·h) when influent concentration of COD and NH4+-N was 300mg/L and 40mg/L, respectively. In addition, various influent Nitrogen and organic shock loading experimentations cure explained that operational conditions showed no obvious effect on INT-ETS variation rule, however, the time of the appearance of feature points marking different reaction phase was influenced.