This paper presents an efficient algorithm for incremental buffer insertion and module resizing for a full-placed floorplan. Our algorithm offers a method to use the white space in a given floorplan to resize modules and insert buffers, and at the same time keeps the resultant floorplan as close to the original one as possible. Both the buffer insertion and module resizing are modeled as geometric programming problems, and can be solved extremely efficiently using new developed solution methods. The experimental results suggest that the the wire length difference between the initial floorplan and result are quite small (less than 5%), and the global structure of the initial floorplan are preserved very well.