Abstract: To meet the requirement for the straightening accuracy of hi-precision light-wall steel tubes,an angle-changeble supporting-block is newly developed.With a new design,contact type of the supporting-block with the tube is changed from the conventional plane-contact into an arc surface-contact,and the angle of the contact surface with the tube can also be changed freely.Thanks to the said design,during the straightening process,the contact surface between the tube and the supporting-block is remarkably increased so as to effectively prevent possible deformation of the tube due to excessive stress concentration.Relevant operation practice shows that with the new type supporting-block,the straightening qualification rate can be enhanced from the original approxi.60% to over 90%,which would get both the economic benefit and the productivity increased obviously.