Field emission cathode plays an important role in the development of vacuum electron devices. In competition with solid-state devices, vacuum electron devices develop sustainably towards high frequency and high power. Field emission cathodes make it more practical to improve the size, the reliability, the power consumption and the operating frequency, etc. This article reviews the recent development of the high-current-density field emission cathodes. Especially, experimental results show that the emission current density of carbon nanotube field emission cathode is up to A/cm2 stably during a long time, which confirms the possibility to realize the applications in field emission microwave amplifier, free electron lasers and novel neutron source.