Quality of Service (QoS) is applied to evaluate the satisfaction level of users using a service and it is a measure and evaluation of the service level of service providers. As one of the significant contents of grid technologies, the QoS has gradually become a focus of current Internet researches. The grid is a network infrastructure that can aggregate decentralized resources to form a higher-level distributed resource sharing environment; the highly dynamic performance presented by the grid system is caused by resource competition and task uncertainty and providing extraordinary QoS is one of the three criteria for evaluating the grid technologies. Bayesian network is a method of graphing knowledge and is a probabilistic model which can be calculated; data from various sources can be synthesized and comprehensively reasoned through this Bayesian network. On the basis of summarizing and analyzing previous research works, this paper expounds the development background, current situation and future challenges of Bayesian network technology, presents the studying status and existing problems of grid QoS trustworthiness evaluation, introduces network optimization analysis method and QoS trustworthiness evaluation algorithm, proposes the Bayesian network-based trustworthiness model, effectiveness function and grid QoS evaluation reasoning process, therefore, establishes grid QoS trustworthiness evaluation model and analyzes Bayesian networkbased QoS trustworthiness evaluation mechanism. The simulation results show that the proposed method can enhance the trustworthiness of service information and improve the rationality of service matching in a dynamic service grid environment. The study results of this paper provide a reference for the further researches on the grid QoS trustworthiness evaluation based on Bayesian network. INDEX TERMS Quality of Service (QoS), Bayesian network, trustworthiness evaluation, simulation experiment.