In this paper, we studied a new type of underactuated elephant trunk robot(the ET robot) used unconventional scissors mechanism, and put forward a kind of method in order to make the mechanics calculation of the scissors mechanism easier. Using this method can remarkably reduce the analysis work of the mechanics calculation, improve the efficiency of analysis, and highly reductive motion of the robot. To verify the validity of the simplified method, we used the automatic dynamic analysis of mechanical systems-the ADAMS to carry an simulation of the ET robot when grab a cylinder before and after use the simplified method....