The high coercivity of 26.2 kOe for SmCo5 nanoflakes are obtained by multistep (three steps) surfactant-assisted ball milling. The magnetic properties, phase structure and morphology are studied by VSM, XRD and SEM, respectively. The results demonstrate that the three step ball-milling can keep more complete crystallinity (relatively less defects) during the process of milling compared with one step high energy ball-milling, which enhances the texture degree and coercivity. In addition, the mechanism of coercivity are also studied by the temperature dependence of demagnetization curves for aligned SmCo5 nanoflakes/resin composite, the result indicates that the magnetization reversal could be controlled by co-existed mechanisms of pinning and nucleation.