A pre-magnetization method of a marine transformer based on cascaded small-capacity transformers is characterized in that a ship-mounted transformer connected with shore power system is used for pre-magnetizing the main transformer arranged between the medium voltage bus bar and the low voltage bus bar, and the main transformer is respectively connected with the medium voltage bus bar and the lowvoltage bus bar through a switch; the ship-mounted transformer is connected with the medium-voltage bus bar and the low-voltage bus bar respectively, and the capacity of the onshore transformer is smaller than that of the main transformer. The invention has the advantages of small overall investment, low realization difficulty, excellent inrush current suppression effect, low operation difficultyof the equipment, low debugging difficulty when on-line, and convenient use.