The frequency range of the millimeter wave is from 30 up to 300 GHz. Millimeter waves have been extensively studied for many applications including high resolution radars, communications, materials processing, plasma heating, high energy particle accelerators and power transmission. In this paper, an injection-locked millimeter wave oscillator based on field-emission cathodes is proposed and demonstrated the well phase/frequency controllability. The simulation results are consistent with the prediction of Adler's equation. The preliminary results show that the design of the injection-locked oscillator seems to promise useful and compact millimeter wave sources.