Voltage island has become a very effective design style for power saving by utilizing different supply voltages for different modules. However, the new style also brings forward some new challenges, especially to the designer of P/G networks. In this paper, we study the power delivery problem in voltage island designs, and propose to consider voltage drop during the floorplanning process to avoid design iterations. We have implemented a floorplanner supporting voltage islands, with special considerations on power delivery integrity. Our analysis shows that it is unnecessary to design the pitch of the network in order to guide the floorplanner. Experimental results have demonstrated the effectiveness of our approach.