In order to obtain low phase noise planar oscillator, the common resonator and phase noise optimization method in push-push oscillators are studied in this paper. Firstly, a differential transmission line loaded by a coupled-pair of multiple split ring resonators is proposed to achieve weak coupling between two sub-oscillators, and the frequency selectivity of common resonator is improved. Then an X-band push-push oscillator utilizing this structure is designed and realized, and a phase noise optimization method based on active quality factor of oscillator is adopted in the design. The measured phase noise is -115.48 dBc/Hz@100 kHz offset at the second harmonic frequency of 9.52 GHz, and the suppression of fundamental frequency component achieves -54.55 dBc.