Abstract: To reduce the vibration during the operation of air conditioner, geometric models of the pipe system connected to refrigeration compressor and the gas column in pipe system were created by Pro/Engineering software, and the modal analysis based on ANSYS software was carried out to obtain the first six-order natural frequencies of the pipe system and the gas column. Results show that the fourth natural frequency of the pipe system is very close to the compressor excitation frequency, and resonance occurs. Because the natural frequencies of the gas columns in suction pipe and discharge pipe are not in the resonance region, the gas columns in the suction pipe and discharge pipe cannot resonate. For the problem of pipe system resonance, the vibration characteristics of the pipe system with different lengths of the suction pipe, different lengths of discharge pipe and fixed supporting number are analyzed. The modal analysis results show that the natural frequencies of the pipe system and the gas column in the pipe system increase with the decrease of suction pipe length and discharge pipe length. When the rational value of the suction pipe length is taken, the natural frequencies of the pipe system and the gas column are not in resonance region, and resonance cannot occur. With the decrease of discharge pipe length and the increase of the fixed supporting number, the natural frequency of the pipe system gradually gets far away from the resonance region, which is beneficial to avoid resonance. Additionally, it is reasonable to set two fixed supportings for the pipe system if considering the convenience for operation and economic condition. Simulation results accord with the reported experiment results.