When a bug was reported to the bug tracking system, it should be assigned to a developer who is responsible for its resolution after it is confirmed. This processing is called bug triage. With increasing number of bug reports submitted to the bug tracking system, it is more and more difficult to assign appropriate developers to the reported bugs manually. In this paper, we propose an approach called BUTTER (BUg Triage by topic modeling and heTERogeneous network analysis) to automatically assign bugs to developers. Different from existing work, BUTTER not only uses topic model to analyze the text information from bug reports, but also innovatively takes structural information into consideration by constructing a heterogeneous network which includes relationships among submitters, bugs and developers. Experiment shows that BUTTER outperforms other methods on automated bug triage.