In order to achieve high-efficiency alkali conversion and impurity removal of high titanium slag under the condition of low alkali concentration, a new way of oxygen-rich alkali conversion in KOH solution was proposed. The conversion law of element occurrence state and the influence of the conversion conditions on the titanium conversion rate and removal rate of silicon and aluminum were studied. The results showed that the KOH solution converted the titanium oxide in high titanium slag into whisker-like potassium titanate. Silicon and aluminum elements were dissolved into the solution. Under the following conditions, KOH concentration of 6 mol/L, conversion temperature of 260 °C, initial oxygen partial pressure of 2 MPa, liquid-solid ratio of 35 mL/g, conversion time of 4 h, and high titanium slag particle size of 48-74 μm, the conversion rate of titanium was 97.0%, and the removal rates of silicon and aluminum were 90.2% and 76.2%, respectively. Oxygen-rich alkali conversion product was converted to rutile with a TiO₂ grade of 99.1% by acid hydrolysis conversion.