With the development of the cloud computing, its security issues have got more and more attention. There is a great demand for the examining the content of data or packets in order to improve cloud security. In this paper, we propose a new algorithm about pattern matching for cloud security named Bit-Reduced automaton, First it performs inexact matching to filter out the part of nonattack information and then do exact matching to get the final attack information. Finally, Bit-Reduced automaton is feasible through a preliminary evaluation.