In selecting the auditors most suitable for their needs, a firm will focus on the choice of the competitors and seek a trade off between the benefit of audit expertise and the protection of the proprietary information spillovers. This paper uses sales ranking and the similarity of business scope to measure industry rivals, and examines the auditor sharing behavior among close competitors. It finds that rival firms are reluctant to engage the same auditor when their business scope is more similar, and this negative relation is greater when the rival firms operate in a highly competitive industry. If an external auditor is an expert, it will change the tendency of competitors not willing to share auditors. In terms of economic consequences, peer firms sharing the same auditor have a similar economic decision. This research constructs a method to measure the competitors from the financial perspective, validates the problem of sharing auditors among competitors, and finds that auditors are not only the assurance providers, but also the information intermediaries and rich information sources.