Abstract: Emerging with open environments, the software paradigms, such as open resource coalition and Internetware, present several novel characteristics including user-centric, non-central control, and continual evolution. The goal of obtaining high confidence on such systems is more difficult to achieve. The general developer-oriented metrics and testing-based methods which are adopted in the traditional measurement for high confidence software seem to be infeasible in the new situation. Firstly, the software development is changed from the developer-centric to user-centric, while user's opinions are usually subjective, and cannot be generalized in one objective metric. Secondly, there is non-central control to guarantee the testing on components which formed the software system, and continual evolution makes it impossible to test on the whole software system. Therefore, this paper proposes a trust-based approach that consists of three sequential sub-stages: 1) describing metrics for confidence estimation from users; 2) estimating the confidence of the components based on the quantitative information from the trusted recommenders; 3) estimating the confidence of the whole software system based on the component confidences and their interactions, as well as attempts to make a step toward a reasonable and effective method for confidence estimation of the software system in open environments.