In this study, magnetic properties of the strontium ferrite were theoretically investigated by Ab initio (first principle) method. The influences of various additives on the magnetic properties of the strontium ferrite were analyzed to designed new composition of the strontium ferrite system with high magnetic characteristics. As shown in the results, the total magnetization of the strontium ferrite was $42.55M_B$. Based on the DOS results, the magnetic characteristics of the strontium ferrite were mainly influenced by Fe atoms at 6 positions in the unit cell. Also the La-Mn strontium ferrite has the superior magnetic property than the Mn strontium ferrite.