Based on the phenomenon of the sharp decrease of H2S concentration in biogas during high solid anaerobic digestion (HSAD), the potential inhibitors of H2S production and their impact upon the stability of digesters during waste activated sludge (WAS) anaerobic digestion (AD) were evaluated. The results showed that H2S concentration in biogas decreased over 80% during HSAD compared to conventional AD. The results of biochemical methane potential tests indicated NH4Cl at a dosage ratio of 2.50 g.L-1 was determined as the optimum inhibitor of H2S in-situ prevention (ISP). H2S concentration in conventional AD decreased by over 45% at the same NH4Cl dosage ratio. Subsequent stable biogas yield under a small fluctuation of pH and biogas components in digesters revealed that the stability of digester was not affected. NH4Cl dosage showed an H2S ISP effect during WAS conventional AD under the condition that AD reactors were stable.