Many manufacturers and researchers have established various Intrusion Detection System (IDS) evaluation standards, most of which involve tests of IDS functions but neglect evaluation of IDS security. On the basis of IDS security evaluation, this paper describes segmented and multi-level mixed evaluation methods, classifies intrusions by type of TCP/IP, and illustrates the evaluation process by means of the Deterministic Finite Automaton (DFA) in fragmentation, making the test process more straightforward and vivid. Credibility levels are assigned to measures which are taken to make products meet basic functional requirements, thus dividing the evaluation process into three levels. © 2011 IEEE.