The classical string matching algorithms are facing a great challenge on speed due to the rapid growth of information on Internet. Meanwhile, multi-core CPU has been widespread on computers. But classical string matching algorithms does not apply to multi-core CPU flexibly. It not only affects the run-time speed, but also makes a waste of the resource on CPU. In this paper, we proposed a parallel string matching algorithm based on DFA, it solved the problem effectively. By classification on the first letter of each pattern, all CPU cores could work at the same time, which do not conflict. Experiments demonstrate whether the hit rate is high or low, the algorithm has an ideal performance.