Conversion-type materials attract increasing attention for rechargeable batteries because of their high energy density compared with intercalation-type materials. However, the development of conversion materials for sodium and potassium ion batteries is in its beginnings, and a few materials have been studied. In this study, high-throughput computational screening was performed to discover high energy density conversion cathode materials for sodium and potassium batteries. Conversion reactions of cathode materials were examined using the Materials Project database. The reaction voltage curves as a function of specific capacity were obtained using grand potential phase diagram. The calculation results indicated that fluorides, chlorides, bromides, and oxides are promising conversion cathode materials, exhibiting high reaction potential and capacity. The average reaction potentials of sulfides, selenides, phosphides, and nitrides indicated that they are not appropriate materials for conversion cathodes.