By improving the circuit structure and adopting the CMOS cross-coupled structure to provide negative resistance, a 20 MHz integrated quartz crystal oscillator was proposed. In this oscillator, the common-mode feedback was adopted to achieve stable DC output, and the RC high filter circuit and the pre-rejection circuit were designed to reduce the phase noise. With NUVOTON 0.35 μm CMOS process, the circuit was designed and simulated by the Spectre in Cadence. Under the supply voltage of 3.3 V and the bias current of 400 μA, the results indicated that start-up time of the oscillator was about 1.5 ms, the peak value of the output waveform was 1.08 V, the DC output was about 801.6 mV, the frequency of output was 20 MHz, and the phase noise reaches -155 dBc/Hz@1 kHz and -164 dBc/Hz@10 kHz, respectively.