In view of the existing problems of current picking manipulator, an articulated picking manipulator with four degree of freedom was developed. In order to harvest fruits and vegetables of the target space flexibly and efficiently, meanwhile to reduce operating space and structure size of the manipulator as much as possible, the general structure optimization method of the articulated manipulator for picking fruits and vegetables was proposed, which was applied in random cube of the picking space. The mathematical models were constructed by taking the workspace for constraints, and the Matlab optimization Toolbox was applied to realize the proposed method. For verifying the availability of the method, the structure parameters of the designed articulated picking manipulator were optimized by referring to the example of the cucumber picking operation in greenhouse; and the motion planning experiments of the optimized manipulator were carried out. Experimental results showed that the optimized manipulator could cover the whole required target space of the cucumber harvesting operation, and also could reach the limit points and other picking points of the target space, the maximum positioning errors of the x,y,z axis were respectively 4.3 mm,5.6 mm,6.8 mm, so it could basically satisfy the requirement of the cucumber picking operation. 