Abstract: Studied are the main aspects of the SEW hi-collapse-resistant casings made in 80~125 ksi grade steel, including material properties, dimensional accuracy, residual stress and resistance against external collapse, etc.The study result reveals that the yield strength is the determining factor affecting the collapse resistance of the SEW casing, while other factors such as DS ratio, outer roundness, wall thickness unevenness rate and residual stress act as the main elements affecting the anti-collapse strength of the casing. Accordingly, properties against external collapse of the SEW casings are expected to be improved by means of enhancing yield strength and dimensional accuracy, and reducing DS ratio and residual stress.