The microstructural evolutions of 7055 aluminum alloy after single and two-step homogenization with or without applying 12T high magnetic field were investigated. The as-cast microstructures of 7055 alloy consist of α+AlZnMgCu eutectics, Al7Cu2Fe phase and AlTiCuFe phase. During homogenization, coarse α+AlZnMgCu eutectics located at interdendritic region become smaller, discontinuous and spheroidized, some of them transform into Al2CuMg (S) having a higher melting point. High magnetic field significantly accelerates the dissolution of α+AlZnMgCu eutectics and S phase. The least amount of α+AlZnMgCu eutectics and S phase is obtained when the alloy homogenized at 4650C/10h+4850C/8h under 12T high magnetic field.