This paper presents a new flow to handle fixed-outline floorplanning for mixed size modules. It consists of two stages, which include global distribution stage and legalization stage. The methodology is very flexible, which can be integrated into other methods or be extended to handle other constraints such as routability or thermal issue. The global distribution stage aims to obtain better wirelength while distributing modules over a fixed outline. Once a good result can be obtained in the first stage, the legalization stage only needs to obtain a feasible solution by maintaining the good result. The legalization is performed by curve merging in a slicing tree, which is obtained by the partition based approach. Two functions are proposed to divide a circuit and the associated placement region into two parts. Although the fixed-outline floorplanning with mixed size modules is very difficult, our method still can obtain better results. The experimental results show that our method can averagely reduce wirelength by 22.5% and 4.7% than PATOMA  and DeFer  in mixed size benchmarks.