Abstract: The mechanism and complexity of the conversion algorithm from nondeterministic finite automata (NFA) to deterministic finite automata (DFA) were studied, and a great number of repeated traversal and invalid traversal phenomenon in the well known SUBSET algorithm were especially studied. An improved MF-SUBSET algorithm was proposed to solve the above problem. The simulation results indicated that the present searching strategy could be decided by the proposed MF-SUBSET algorithm through increasing status flags and traversal path flags, which could obviously avoid the repeated traversal and invalid traversal operation and effectively improve the conversion efficiency.