We investigate the non-Markovian behavior in open quantum systems from an information-theoretic perspective.Our main tool is the max-relative entropy,which quantifies the maximum probability with which a state p can appear in a convex decomposition of a state σ.This operational interpretation provides a new view for the non-Markovian process.We also find that max-relative entropy can be the witness and measure of non-Markovian processes.As applications,some examples are also given and compared with other measures in this paper.