Abstract: Discussed in the article is the straightening blind area as encountered with during the operations of both the typical cross-roll straightener and the opposed-roll straightener. And also analyzed are the formation reasons， location and size of such blind area of these two types of straighteners. Other elements which affect the range of the blind area are analyzed，too，including roll space，working length of the roll，and rolling overlap coefficient，etc. As a result，methods for reducing the blind area and improving the pipe straightening quality are proposed.