Objective: To fix optimum extracting craft of polysaccharides in Siwu Decoction.(Radix Rehmanniae Preparata, Radix Angelicae Sinensis, Radix Paeoniae Alba, Rhizoma Chuanxiong). Methods: The orthogonal design was used and refluxing time (A). water totalling (B) and extraction time (C) were defined as factors of the design. Results: A factor and C factor had notable influence on the content of polysaccharides. Conclusion: Optimum extracting craft was defined as follows: A 2B 1C 2.