Abstract: The edge cracking causes of hot rolled strips produced by CSP were investigated by optical microscope (OM), scanning electron microscope (SEM), transmittion electron microscope (TEM) and energy-dispersive X-ray analysis (EDX). The results indicated that deep oscillations of thin slabs were the origin of the edge cracks of hot rolled strips and AIN precipitates around the prior austenite grain boundaries due to intensive cooling rate rendered the slabs more susceptible to cracks. After seven rolling stands, the transverse cracks of the slabs would propagate to serrated edge cracks, even drop-out type cracks of hot rolled strips.