Topic island on Internet Web pages has seriously affected the performance of focused crawlers. The metric of setting more initial links to find new topics cannot guarantee the comprehensiveness of Web pages. On the basis of analyzing typical crawling strategies and taking into account the hierarchy of topic relevant, we propose a crawling strategy using dynamic tunneling. The crawling strategy uses the tunneling technology based on the topic of Web pages to discover new topics, and constructs a hierarchical topic model to solve the problem of weak link between two topic islands. Meanwhile, the strategy can effectively prevent topic drift caused by collecting too many topic-independent pages, thus dynamic controls the tunneling depth in the crawling direction with the semantic information of the topic maintained. Experimental results show that the proposed method can better address the topic island issue, thereby enhancing the recall of focused search engines.