Industrial robots have been wildly used in machining applications due to its high flexibility, high automationlevel and lowcost. However, the relatively low stiffness of robots seriously influences their machining accuracy and quality. This paper built a singularity measurement model of the robot posture under the constraint of joint-limits. Based on the robotic static stiffness model, a comprehensive robotic stiffness performance evaluation method was proposed. Finally, on the basis of redundant degree of freedom, an off-line machining configuration optimization method of six-revolute serial robots was addressed, which far away from singularity and joint-limits meanwhile achieved the optimum stiffness. Themethod could improve robotic kinematics performance and machining quality effectively through machining experiment.