The catalyst has compound of Co and Mo as active component and oxide of alkali metal as assistant, and its carrier has compound of Ti as main component and oxide of Al, Mg or other alkali earth metals as skeleton material, into which rare earth compound and/or alkali earth metal compound are added as hydration resisting assistant. During the preparation, the carrier skeleton material is first modified with hydration resisting assistant and then mixed with the compound of Ti as main component, and the carrier is finally soaked with the active component. The catalyst has excellent hydration resisting performance and structural stability.