The target movement range of planar five-bar parallel robot is decided by the length of each bar and swinging angle. In general designs are bound by the single-objective optimization. Scope of the overall movement is considered as the goal of optimization. Although this method may seek all the possible movement scope completely, but has actually neglected the restraint of mechanical hinge structure. To determine the length in this way there are interference and stuck phenomenon. To address this issue in this paper the bounds of mechanical structure are added in. A new set of optimization algorithms is established. Analytical method is used to establish the algorithm of planar five-bar parallel robot’s positive solution. Then MATLAB is used to obtain the positive solutions of target movement range. Generally under unconstrained circumstances, we found that there are two positive solutions and mutual symmetry on the x-axis. After adding in the restriction of swinging angle, we succeed in finding the optimal solutions. Finally we use an example to explain how it works. MATLAB is used to determine the length of each bar and found a 200 x 150 mm of the target movement range. Through the diagram has been plotted by MATLAB, we find that the second solution is the optimal solution. This method can be used to optimize the length of planar five-bar parallel robot.