Compared to fully commercialized nitride blue light light emitting diode (LED), the external quantum efficiency (EQE) of current Aluminum gallium nitride (AlGaN) based deep ultraviolet LED is still at a relatively low level. This review first introduces the current development status of AlGaN based deep ultraviolet LED and analyzes the reasons for low EQE. Then, the research progress in improving the EQE direction of AlGaN based deep ultraviolet LED in recent years is elaborated from three aspects: carrier injection efficiency, carrier radiation recombination efficiency, and light extraction efficiency. Finally, the current challenges and future development opportunities of AlGaN based deep ultraviolet LED were discussed.