<p>Enhancing the stiffness of thin floor parts can effectively suppress the chatter, thus improving the machining efficiency and quality. As the application of external auxiliary means like fixtures still face challenges of high cost and poor adaptability, process optimization methods based on the workpiece itself like optimizing allowance distribution or adding sacrificial structures have received increasing attention. However, few studies have investigated its influence on the dynamic characteristics and milling stability of thin floor parts. To this end, this paper proposes a stability improvement method by optimizing the process structure in the milling process. Initially, dynamic characteristics of thin floor parts are simulated, based on which a process structure with variable thickness is presented and effects of structure sizes on the dynamic characteristic are investigated. Further, optimal structure sizes are determined by maximizing the modal stiffness of the weak area. Then, the dynamic model of thin-floor milling is established to determine the milling stability limit and evaluate the improvement of process structure. A series of simulations and experiments are conducted by using the typical thin floor parts as the research object to verify the proposed method. Results show that the stability limit of the workpiece with process structure increases, effectively avoiding the chatter and improving the surface quality.</p>