Abstract: With the fast development of VLSI technology and rapid increase of scale of chip,especially in the design of SOC,the original pattern of placing all PADs on predefined positions is infeasible to ensure high-quality power supply to each individual circuit blocks.In many cases,post-floor planning power supply optimization is also unable to guarantee high-quality power supply under limited routing resources.Therefore,a new pattern that PADs are arranged to be put on any position all around the chip or even on the top of modules comes forth.In this paper,we present a method to allocate optimal floating PADs in tree-mode.Testing with examples of MCNC,we find the result of optimization is evident.