The semi-molten smelting process of a mixture of saprolitic and limonitic laterite ores was systematically investigated and the effect of slag basicity was deeply analyzed. The results indicate that the slag system can be located in the liquidus region of low melting-point diopside (CaMgSi₂O₆) when slag basicity is kept at 0.3 and limonitic laterite mass fraction is not less than 10%. When the reduction temperature, C/O mass ratio, limonitic laterite mass fraction and slag basicity are kept at the optimum values of 1300 °C, 0.86, 20% and 0.3, respectively, ferronickel products with grades 6.42% Ni and 86.99% Fe are prepared. The recovery rates of Ni and Fe reach 88.60% and 72.25%, respectively.