The invention provides a process for refining molten iron by directly using low-grade iron ores. The process comprises the following steps that: 1, low-grade iron ores are magnetically roasted in a fluidized bed reactor to obtain iron ores with stronger magnetism; 2, the fine ores obtained after roasting enter a hot magnetic separator to obtain hot iron ores with higher grade by hot magnetic separation; 3, the high-quality hot iron ores, which are obtained by magnetic separation, are added into a pre-reduction multi-stage fluidized bed to obtain pre-reduction iron ores with a higher reduction degree, wherein the pre-reduction multi-stage fluidized bed is combined by a 2 to 4-stages circulating fluidize bed and a bubbling fluidized bed reactor, and after being reduced by the pre-reduction multi-stage fluidized bed, the metallization rate of the fine ores is over 60 percent; and 4, the pre-reduced iron ores are directly injected in a final reduction furnace or fusion gasification furnace by a hot-pressed block for final reduction refining so as to obtain the molten iron. In the process, the refining process of the low-grade iron ores is completed by fully using energy in the technological process and the low-grade iron ores avoids repeated heating and cooling when being refined into the molten iron, so the energy consumption is greatly reduced.