Abstract: A detail structure analysis about ZT-A series A-frame was done by using computer program and stress measurement.The state of stress in the derrick structure has been made clear when the derrick is loaded by horrizontal,vertical and eccentric loads.Accoreing to the results of analysis,some improvment opinions on design of the derrick were raiaed.In the paper, the importance of the rope is discussed.In the last,it is pointed out that how to use the A-frame in the field operation is best.