To enable pressure impregnation of molten metal even under low pressure by specifying the average particle size of granules and the volume ratio of the reinforcing fiber included in a preform.

In this method, a bulk 2 of a reinforcing fiber 1 is first dispersed in a proper solvent 4 in a container 3, to which a binder is added and stirred to prepare a slurry 6. Then the slurry 6 is spray dried to obtain granules 7. In the granules 7, the reinforcing fiber 1 is dispersed with random orientation in every direction in a three-dimensional space. Then the granules 7 are subjected to dry pressure forming in a die 8 to obtain a preform P. In this method, the average particle size of the granules 7 is specified to ≥10 times as the diameter of the reinforcing fiber 1 and the volume ratio of the reinforcing fiber 1 in the preform P is controlled to ≤40% so that the permeability of the preform P is limited to control the permeation process of a molten metal by pressure impregnation in the preform P. Thereby, a molten metal can be preferentially permeated to the bottom of the preform before the molten metal impregnates in the granules.