The present invention relates to a method for pretreatment of molten iron, which uses a single converter type refining furnace to continuously perform desiliconization and dephosphorization of molten iron with an intermediate slagging process, in which a sufficient amount of The slag is quickly discharged out of the furnace, and sufficient dephosphorization treatment can be performed in terms of cost and quality. The pretreatment method of the present invention includes: a desiliconization treatment process, supplying a gaseous oxygen source to the molten iron (5) in the converter type refining furnace (1) from a top blowing lance (2) to desiliconize the molten iron; a slagging process, At least a part of the slag generated in the desiliconization process is discharged from the converter type refining furnace; in the dephosphorization process, after the slagging process, a CaO-based flux is added to the converter type refining furnace, and a gaseous oxygen source is supplied from the top blowing lance , dephosphorize the remaining molten iron, wherein, in the desiliconization process, the slag height in the furnace is measured, and the measured slag height is defined by the distance from the molten iron bath surface in the furnace to the furnace mouth The desiliconization process is completed in a state where the height ratio of the melting chamber in the furnace is in a predetermined range.