Abstract: Since supply voltage directly determines the chip performance, it is important to take the supply voltage as the design constraint at all IC design stage.Owing to the mammoth complexity of power /ground (P/G) analysis, the supply voltage has not been considered in the placement though it became a constraint of the floor-planning.Different from the traditional global analysis algorithms such as ICCG and SOR, localized successive over-relaxation method (SORPECO) is proposed in the paper.SORPECO is the first try to efficiently analyze P/G voltage distribution in ECO placements.Based on the P/G voltage distribution of previous placement solution, SORPECO can obtain a new P/G voltage distribution only through relaxing small local area surrounding some slight changes in a tentative solution.Thanks to the locality of P G network analysis, SORPECO is of advantages such as locality, efficiency, and high accuracy.In comparison with the traditional efficient ICCG algorithm usually used in floor-planning, experimental results show that SORPECO is two orders of magnitudes faster with ignored accuracy loss (maximum errors <0.062%) .