Design and characteristics of a light source of multiple optical millimeter waves, based on optical phase modulation within an active fiber ring resonator, is theoretically studied. With balanced and optimal design of phase modulation index, the coupling coefficient of input-output coupler, the net loss of the resonator, and the bandwidth of the bandpass filter, 48 40 GHz optical millimeter waves with acceptable amplitude uniformity can be obtained. Effect of initial phase noise of optical millimeter waves on its frequency bandwidth is analyzed. The frequency bandwidth may be less than 100 Hz if the linewidth of input laser and the resonator length are less than 100 KHz and 4 m, respectively. The relation between the waves′ amplitude variation and fluctuation of the index, optical amplifier gain, and the resonator length are given.