Mining sequential pattern is an important topic in the data mining research. In this paper, on the basis of recording the Ctid scheme of the set in every frequent set, the authors propose an algorithm named ISP for mining sequential pattern. In the algorithm the items and the sequence are discussed respectively, and the time join method is used to introduce the candidate sets, so the frequent sets can be gotten. The ISP algorithm takes full use of the existing and updated Ctid scheme, therefore the efficiency of the process is increased besides guaranteeing the validity of the algorithm. Comparing with the algorithm named IMSP,more efficient rules are obtained.