The settling property, COD removal rate, Ca 2+ retention rate, variations of biofacies and the effect of sludge reduction of the high hardness wastewater of the activated sludge process by adding green and safe scale inhibitor PESA (Polyepoxysuccinic Acid) during the experiment have been studied for the COD was 100～300 mg/L, calcium concentration was 110～280 mg/L of the high hardness of wastewater. The results show that MLSS was less than the ordinary activated sludge reactor, the content of the inorganic substrate in activated sludge was significantly reduced and resulted in the decrease of calcium activated sludge putout, the reduction reached to 41.33%, The purpose of calcium wastewater treatment sludge reduction was achieved.The COD removal rate of PESA activated sludge reactor reached above 90%, the Ca 2+ retention rate reached above 80%. PESA inhibits the sedimentation of a part of calcium salt in activated sludge surface, bioactivity was kept well, and in this concentration range, indicative microbial were able to grow and reproduce. The ability to resist impact load has been enhanced in high hardness water, sludge age extension.