After decades of development, high silicon austenitic stainless steels are widely concerned about due to their excellent corrosion resistance and good mechanical properties. Till now, 4%Si high silicon stainless steel has been widely used, but it is not doing well under the condition of high temperature and strong oxidizing medium. 6%Si high silicon austenitic stainless steels can resist in the strong oxidizing medium when the temperature is up to 100 ℃. But the increasing of Si may lead to the increasing of precipitation such as bcc phase, which may cause hot cracks during heat processing. As a result, obtaining a temperature range which is without precipitation is essential. The bcc phase evolution mechanism of 6%Si as-cast high silicon austenitic stainless steel under different solid solution treatment temperature was investigated by means of OM, SEM, XRD and TEM in this work. In order to study the precipitation and re-dissolution of bcc phase, the distribution of alloy elements, morphology and crystal structure of the bcc phase were analyzed under different solution treatments. Moreover, the heat-treated schedules were made based on the experimental results. The results indicated that the solid solution treatment temperatures had a great influence on the microstructure of 6%Si high silicon austenitic stainless steel. The precipitates existed in the as-cast structure were mainly bcc phase with a lattice constant of 0.8747 nm, rich in Mo, Si and Ni elements, and distributed in grain interior and grain boundary. The bcc phase redissolved during the solution when the temperature was between 1050~1200 ℃ for 2 h. The contents of Mo, Si and Ni increased with the rising solution temperature. Furthermore, the bcc phase re-precipitated when the test specimen was heat treated at 1250 ℃ for 2 h. The re-precipitated phase has the same composition with that in the as-cast structure. Thus the optimal solid solution treatment temperature of 6%Si high silicon austenitic stainless is 1100~1200 ℃ for 2 h.