Abstract: This paper presents a method of expressing robot's dexterity at a given point by combining dexterity ofcnd-effector rotation with dexterity of main sections which are perpendicular to each other.It's intuitive,convenient and easy to solve and apply.When using this method to study dexterity of work space of robotwith structural restraint,we found there are different dexterity regions,surfaces and curves.Especially,thispaper presents a concept called pro-set pose of a tool Also we prove that when pre-set pose is changed,thework possibi lity can be greatly improved and that condition of manipulator's dexterity is not changed by a5R manipulator.This conclusion is useful for practical application of a robot.