The invention provides a method for melting and digesting free calcium oxide in converter slag. The method comprises the steps that SiO2 and molten blast furnace slag are added into the converter slag by serving as calcium stabilizers at the temperature of 1,450 DEG C or above, and melt blending is conducted according to a certain weight proportion, wherein the adding amount of SiO2 accounts for 8%-50% of the amount of the treated converter slag, the adding amount of the molten blast furnace slag accounts for 30%-100% of the amount of the treated converter slag, SiO2 and the molten blast furnace slag can be added in an echelon mode or added simultaneously, and constant-temperature digesting is conducted for at least 5 minutes in each echelon of the digesting process, so that full and uniform mixing is guaranteed, entire melt blending is completed within 30 minutes, and water cooling or air cooling can be adopted as the cooling mode. According to the method, the content of free calcium oxide in the improved molten mixed slag reaches the national standard, w(CaO) / w(SiO2) is moderate, the size stability is good, comprehensive resource utilization of solid metallurgy waste is achieved, and more ways are developed for energy saving and consumption reducing of a metallurgy enterprise.