This paper is to study how presence of cracks affects ground-based vibration response of a spinning cyclic symmetric rotor via a numerical simulation. A reference system used in this study is a spinning disk with four pairs of brackets, representing a fourfold cyclic symmetric rotor. A crack with a variable depth is introduced at one of the eight disk-bracket interfaces. Both radial and circumferential cracks are simulated. The ground-based vibration response of the spinning disk-bracket system is simulated using an algorithm introduced by Shen and Kim published in 2006. Compared with a perfectly cyclic symmetric rotor, the crack introduces additional resonances when the crack size is large enough. Frequencies of these additional resonances can be predicted accurately and may be used as a way to detect presence of cracks.