Present orchard spray equipment is much larger, and both power and pesticide consumption are much higher. To overcome the above deficiency, an orchard symmetric swing mist spraying system was developed. To expand the diameter of mist spraying, a planar-spatial hybrid mechanism was designed firstly by analyzing the configuration of driving point and fulcrum, and degree of freedom. The planar-spatial hybrid mechanism was driven by a DC motor, which consisted of a symmetrical double crank mechanism and different multi-degree joints at driving points and fulcrums to realize spatial swing motion of the two mist sprayers. To simplify the manipulation and avoid the backflow of pesticide, a MCU control system was designed to realize one-button start/stop operation of the complex action process of the symmetric swing mist spraying system. According to the orchard’s specification, the structural parameters, including the length of the crank, the height of crank center, height of fulcrum, distance of crank center and distance of fulcrum, were determined by nonlinear programming that took the minimization of machine size and the effective covering of canopy by mist spray as objective and constraint conditions, respectively. And then to achieve the highest efficiency of mist spraying under the constraints of both rate and uniformity of mist spraying, the optimal traveling speed of the machine and rotation speed of the crank were determined. This spraying system can guarantee the effective coverage of crowns within height of 1500~4300mm and 5500mm width with 400mm radius mini mist sprayer, and guarantee the uniformity and quantity for spray of mist spraying on both sides of the trees, whose working efficiency can reach 2.33~2.67hm2/h. It is an energy-saving, pesticide-saving and miniature mobile orchard spraying system and will be a better selection in the future for pest control in orchards.