The volume fraction and carbon content of retained austenite in the austempered high silicon cast steel after various austempering combinations were investigated by XRD method. The experiments indicated that the volume fraction and carbon content of retained austenite are low at lower austempering temperatures, and with the increasing of the austempering temperature the volume fraction and carbon content of retained austenite increase gradually within the 240-400 ℃ of austempering temperature. It has been also found that at the beginning of austempering transformation, the volume fraction and carbon content of retained austenite is relatively low and with the extending of the austempering time, the volume fraction and carbon content of retained austenite increase gradually. Austempering afer 60 minutes the volume fraction and carbon content of retained austenite reache to the maximum values and then decrease with the extending of the austempering time within the austempering time given.