Abstract: Surface crack defect were observed on the tail of X52 pipe line steel hot-rolling coil with a thickness of 15.9 mm. The microstructure and chemical composition of the cracks were analyzed by means of optical microscope, scanning electron microscope and energy dispersive spectroscope. The results show that the phenomenon of warping hydrops and poor effect of reverse flushing intercept descaling water in the hot rolling slab of the hot rolling process. This phenomenon leads to the local overcooling of the strip. Therefore, in the process of finishing rolling, the surface deformation of the strip nonuniform so that the pull crack was produced. The crack can be effectively controlled by improving the warping phenomenon of the rough rolling and adjusting the angle of the reverse flushing.