This paper presents a floorplanning method based on particle swarm optimization (PSO). We adopted the B*-tree floorplan structure to generate an initial stage with overlap free for placement and utilized PSO to find out the potential optimal placement solution. Unlike other related research, our method can avoid the solution from falling into the local minimal and has ability of more efficiency and robustness for explored solution space. Experiments employing MCNC and GSRC benchmarks show that the performance of our method for placement by the ability of exploring better solutions. The proposed approach exhibited rapidly convergence and led to more optimal solutions than other related approach.