Abstract. There are increasing numbers of malicious applications in iOS platform, which is a severe threat to the iPhone users. The static analysis and dynamic analysis both play important roles in application security assessment. However, there are a lot of challenges in dynamic analysis technology for iOS applications now. We did some research about the characteristics of the malicious applications and studied the key technologies of the iOS platform. In this paper, we provided some dynamic analysis methods about Keychain access monitoring, encryption and decryption monitoring and UI Web View security monitoring. These methods can discover some vulnerabilities for the iOS applications.