Based on AC algorithm for performing multiple string matching algorithms, two-way AC algorithm was proposed. The algorithm constructs a forward finite automaton and a reversed finite automaton in the preprocessing stage. In the Matching stage it scans the text string from middle to right with a forward finite automaton and concurrently from middle to left with a reversed finite automaton. The algorithm has been implemented by modifying the source code of Snort. The experimental result shows that the time performance of two-way AC algorithm is superior to BM algorithm, WM algorithm and AC algorithm. Efficiency of the algorithm is about 1.5 times AC algorithm if the mode of detection is to discover and stop.