With the widespread use of information systems, traditional manual audit approach cannot adapt to the quick development of information technologies. It has drawbacks of high cost, inefficiency, big risk, poor quality, etc. Computer-assisted audit and its applications are studied in this paper. Firstly, comparative analysis between traditional manual audit and computer-assisted audit is conducted. Then the flow of data-oriented computer-assisted audit is presented and the implementation steps are detailed. Finally, the applications of computer-assisted audit are discussed in four practical audit cases of information systems, i.e. hospital information system, electrical police management system, local taxation management information system and medical insurance fund management information system. And the corresponding audit results are given. The practical audit cases show that computer-assisted audit can expand the audit scope and perform deeper data analysis, thus cutting down the cost and risk of audit while improving efficiency and quality of audit. Therefore, it can effectively help auditors to perform information systems audit.