Crack growth rate, as an important parameter, is widely applied in crack growth evaluation and fatigue life prediction. The objective of this paper is to study crack growth rate with the metal magnetic memory (MMM) technology which is a non-destructive testing method newly developed. The correlation between crack growth rate da / dN and magnetic memory signal Hp(y) is investigated through three-point bending fatigue testing. Samples of steel X45, with different heat treatments, quenching and thermal refining, are tested in HYG fatigue machinery. The correlation curves of da / dN ~ Hp(y) are built and the characteristics of magnetic memory signal are given. The influence of heat treatment on Hp(y) is also analyzed. The crack growth rate model of X45 based on MMM signal is presented and verified.