By solving two-dimensional Reynolds-Averaged Navier-Stokes equation and using two equation SST turbulent models, the two dimensional flow field of an airship is simulated. The influence of airship envelop vibration on the flow field is analyzed. The influence on flow separation and drag of different vibration amplitude, frequency and wave length is analyzed on the hypothesis that a wave is promulgating in the flow direction on the airship envelop upper surface. The results indicate that the vibration can make the airship flow field dramatically change: with fixed vibration amplitude and frequency, reducing wave length will result in flow separation and drag coefficient increase; with fixed wave length and frequency, increasing amplitude will have the same effect; with fixed wave length and amplitude, increasing frequency will induce flow separation and drag coefficient decrease because of the enhancement of unsteady effect. Besides, it also demonstrates that certain form of vibration with suitable vibration correlation parameters may restrain flow separation and reduce drag, which would be an approach for decreasing drag of airship.