Provided are a chemical compound of an isocitrate dehydrogenase inhibitor, and an application thereof, belonging to the field of medicinal chemistry; specifically provided is the chemical compound represented by formula I, or its isomer, pharmaceutically acceptable salt, crystal, solvate, or prodrug, as well as their preparation methods and pharmaceutical compositions containing said chemical compound, and an application of said chemical compound or composition. The chemical compound has very good ability to inhibit mutant IDH2 enzyme activity and to inhibit mutant IDH2 neoplastic cells, and may be used for preventing and/or treating a tumor characterized by the presence of mutant IDH2.