The work aims to enable the bag-delivering packaging machine to pick up and deliver the bags in a more precise and stable manner. By establishing the mathematical model for the bag-picking mechanism, the feasible region of big and small arm hinge coordinates and the initial installation angle range in the allowable space for the packaging machine were obtained. The kinematical parameter analysis formula of the end effector was calculated in the closing-vector-circle method. Its kinematical curve spectrum was obtained and analyzed with Matlab program. After the optimization, when the big arm length l1=360 mm, small arm length l2=200 mm and installation angle =30, the kinematical curve track of the end effector was in a stable transition without sudden change. The bags can be picked up and delivered more stably by adopting the bag-picking mechanism with the optimized structure parameters.