Dependability management is an essential issue for Internetware which is in open, dynamic and decentralized Internet environment. Most research focuses on trust measurement and evolution model. However, there are some issues of the model in the aspects of source of trust, the constraint on trust relation of entities, and the parameter of trust transition for Internetware. This paper proposes a dependable entity model for Internetware, and presents a method of trust measurement based on Bayesian networks. Dependability of entity is secured by mechanism of self-examination and declaration. Trust relation of entities is constrained by contract trust. The parameter of trust transition is calculated accurately by synthesizing recommendation trust and being amended by evaluation. In the last of this paper, we design an experiment and the results show that the model is correct.