The importance of loaded quality factor QL was analyzed and the method of reducing phase noise on the basis of improving QL was performed. The formula of QL was derived from analysis of the Pierce oscillator circuit, and calculated by MATLAB. According to the results, we can draw a conclusion that QL is explicitly related to circuit parameters. Based on this conclusion, the prototype 120MHz crystal oscillator was designed and the experiments were carried out. The crystal resonator we use is AT-cut 5th overtone crystal resonator with UM- 1 resistance welding package, its unloaded quality factor Q0 is about 1.06 × 105. The measurement results of near carrier frequency phase noise are -103dBc/Hz@10Hz and -134dBc/Hz@100Hz. Experimental results show that it is feasible to design low phase noise crystal oscillators based on improving QL.