At present, bug tracking systems are used to collect and manage bug reports in many software projects. As participants, the testers not only submit bug reports to the system, but also comment on bug reports in the system. The tester’s behaviors of submitting and commenting reflect his/her influence in bug tracking systems. However, with the rapid increase of the bug reports in software projects, evaluating the testers’ influence in the projects accurately becomes more and more difficult. Aiming at solving this problem, the submission and comment on bug report can be regarded as social behaviors of the testers, and thus the method of Influence Ranking for Testers (IRfT) in bug tracking systems is presented and used for measuring the influence of the testers in this paper. The case study of the Eclipse project in Bugzilla shows that the result produced by IRfT is consistent with the actual performance of the testers in this project. The ranking results can keep stable in the cases of link adding or removing and tester removing in tester networks, and the results are also proved to be valid in the future. The further investigation on the speed of network break-down by node removal demonstrates that the top-ranking testers are important in the organization of tester networks. Additionally, the results also show that the ranking of the testers is related to the existence time in bug tracking system. Therefore, IRfT is proved to be an effective measurement for evaluating the influence of the testers in bug tracking system, and it can further demonstrate the testers’ contributions in software testing, such as bug validations, bug fixes, etc.