By using an IHMM easy-estimation training algorithm this paper discusses Chinese connected digit speech recognition system with efficient performance, and based on Level Building searching algorithm, whose reference patterns use IHMM mode. The paper describes the theory of the system. It includes its feature-extracting, IHMM mode, training procession, recognition procession, and the experiments that are used for speaker trained, multi-speaker and speaker independent mode. The results of the experiment are analyzed and discussed.