Abstract: The motion of the arms of the SCARA type dual arm robot can be simplified to be the motion of quadrangles. Get the inequality representing the position of the master arm and discretize the boundary of the quadrangles representing the slave arm, then divide the joint space of slave arm into several equal parts and get the Cartesian coordinate of those discretizing point in the Cartesian space corresponding the dividing point. put those coordinates into the inequality and check the inequality to judge if the master arm collide with the slave arm, finally search the collision free point to get the optimal path.