Abstract: According to the idea of extracting harmonic power while phase locking the fundamental,a phase locked W band second harmonic two port Gunn oscillator is developed, with two phase locked loops. The relationship of phase shaking between the signals of millimeter wave and intermediate frequency is analyzed. Meanwhile the limitation of phase noise determined by internal phase locked intermediate frequency is pointed out. The phase locked oscillator, whose output power is over 10 mW and phase noise is -70 dBc/Hz@50 kHz, may be use as local oscillator or others.