The stiffness of a squirrel-cage with local crack was analyzed, and the dynamic characteristics of a rigid rotor system supported by the cracked squirrel-cage were studied. Firstly, the analytical stiffness of the cracked squirrelcage was deduced by static analysis. And then the stiffness was predicted by employing the finite element method (FEM) for the cracked squirrel-cage with different cracked positions and different number of cages. According to the FEM results, a stiffness formula of the cracked squirrel-cage was obtained by use of the least squares fitting. To find out the effects of the cracked squirrelcage on natural frequencies and dynamic characteristics, the theoretical model of the rigid rotor system supported by cracked squirrel-cages was established and simulated. The results show that, when the local crack appears on the squirrel cage, the stiffness of the support decreases, which leads to a decrement in the critical speed. Additionally, the cracked squirrel-cage also can cause a difference between the radial and horizontal stiffness, and thus results in elliptical orbit of shaft center.