Abstract: Studied are the separate influences by three different types of roll gap adjustment systems of the 3-roll mandrel mill(i.e., the side-swing type, the pendulum type and the radial type) on wall thickness accuracy of the pipe as rolled.Comparative analyses are made with the said 3 systems as designed in terms of dynamic behavior, durability and disassembly complexity, etc., which lead to such a conclusion that compared with the other two types, the swing-arm roll gap adjusting system is in possession of better performance indexes, being a mandrel mill roll gap adjusting system with advanced comprehensive performance.