Study on the crystallization process of amorphous (Fe0.99,Mo0.01)78Si9B13(FMSB) alloy with and without solid state reaction at their surfaces were carried out under pressures from 3 to 5 GPa at a temperature range of 510 to 660℃ . When the amorphous FMSB alloy with the reaction was annealed at the temperature range, it is transformed into nanocrystalline α - Fe( Al) at 4 GPa and α - Fe (Mo, Si), (Fe, Mo)3B or Fe2B at other pressures, which were as same as the crystallization products of the amorphous alloy without the reaction at the same pressures. The crystallization mechanism of the amorphous alloy with the reaction was suggested on the basis of therrnodynamic theory and a simple solid model.