Reputation mechanism has been recently introduced into wireless sensor networks(WSNs) to overcome the deficiencies incurred by cryptography alone.Unlike most current reputation mechanisms that are based on binomial distribution and to some extent,do not give due attention to the aspect of energy constraint of WSNs,this research deduces and proves the feasibility that negative binomial distribution can well be used in the reputation update with distinctive energy-saving features.Comparison tests with respect to the energy consumption in terms of reputation computing frequencies are done between the traditional reputation method and the one in this study.Results show that our method can save more energy for the reputation update and thus can better meet the power constraints of WSNs. Reputation mechanism has been recently introduced into wireless sensor networks (WSNs) to overcome the deficiency incurred by cryptography alone. Uniform most current reputation mechanisms that are based on binomial distribution and to some extent, do not give due due to the aspect of energy constraint of WSNs, this research that deducts and proves the feasibility that negative binomial distribution can well be used in the reputation update with distinctive energy-saving features .Comparison tests with respect to the energy consumption in terms of reputation computing frequencies are done between the traditional reputation method and the one in this study. Results show that our method can save more energy for the reputation update and thus can better meet the power constraints of WSNs.