Aiming at the problem of designing secure and efficient user authentication protocols with anonymity for wireless sensor networks, based on the widely accepted assumptions about the capabilities of attackers and using the scenarios-based attacking techniques, the security of two recently proposed two-factor anonymous user authentication schemes for wireless sensor networks was analyzed. The following two aspects were pointed out:1) the protocol suggested by Liu etc. (LIU C, GAO F, MA C, et al. User authentication protocol with anonymity in wireless sensor network. Computer Engineering, 2012, 38(22):99-103) cannot resist against offline password guessing attack as the authors claimed and is also subject to a serious design flaw in usability; 2) the protocol presented by Yan etc. (YAN L, ZHANG S, CHANG Y. A user authentication and key agreement scheme for wireless sensor networks. Journal of Chinese Computer Systems, 2013, 34(10):2342-2344) cannot withstand user impersonation attack and offline password guessing attack as well as fall short of user un-traceability. The analysis results demonstrate that, these two anonymous authentication protocols have serious security flaws, which are not suitable for practical applications in wireless sensor networks.