As　the　performance　of　vacuum　electron　devices　is　essentially　governed　by　the　properties　of　their　cathodes,　developing　efficient　and　durable　thermionic　cathode　is　necessary　and　highly　desired　to　meet　the　boosting　requirements　of　vacuum　electron　devices.　This　review　summarized　the　progress　made　in　the　past　decades　with　a　detailed　discussion　on　the　occurred　various　thermionic　cathodes　and　their　features,　and　the　understandings　of　the　correlation　between　the　emission　properties　and　the　composition,　where　structure　and　synthesis　method　are　well　illustrated.　Furthermore,　dispenser　cathodes　with　novel　structures　and　emission　mechanism　are　highlighted　to　indicate　the　recent　achievement　in　this　area　of　research,　and　Sc-cathode　is　considered　as　a　promising　candidate　for　the　next-generation　vacuum　electron　devices　due　to　the　greatly　improved　efficiency.　However,　challenges　still　exist　to　meet　the　ever-growing　demands　of　thermionic　cathode　with　collaborative　requirement　of　high　performance,　easy　fabrication　and　inadequate　reproducibility.