For the characteristic of compact structure, low inertia, high rigidness and accuracy, parallel mechanisms are worthwhile to be popularized in the field of agricultural robotization, especially in situations that require precise movement in limited space. Focusing on the harvesting task of strawberries in ridge culture, a 4-PPPR robot manipulator with three translational DOF and one rotational DOF is devised in this paper. A type synthesis method of G(F) set theory is used to design its topology structure in 3D space. Compared to traditional machine design methods, this synthesis method allow one to decide the manipulator's configuration in a "Topdown" logic initially from the appointed features of the manipulator's moving platform. A software simulation is carried out to demonstrate this mechanism can meet all the movement requirements by driving the four active joints allocated on the fixed platform.