Abstract: During horizontal direction accelerated walking course of stack-crane,mast will be deflected in vertical direction,which leads to lower access precision especially to high stacks.Single mast stack-crane in lab centre of Xi’an University of Science and Technology was taken as an example.Via building mathematical model of the stack-crane’s mast,deflection of the mast tip was calculated and analyzed.Relation of mast-tip’s deflection and acceleration was simulated by Matlab software.The simulation result showed that the deflection of the mast tip has a parabola relation with the acceleration of horizontal walking approximately under ideal conditions,while bigger deformation would appear in some sections when there is random noise.