In this paper, the dynamic characteristic of Roots blower's shell is analyzed by the ANSYS code. The natural frequencies and the vibration modes of the shell are given. The output of computation shows that the natural frequency of the shell is higher than the fundamental frequency of the rotor system, and the vibration modes of the shell structure are mainly bending, twisting, and their combination. The dynamic analysis of the shell may predict the faults in structural design, and provide some scientific basis for reducing the structural vibration and the noise of the Roots blower.