The modal analysis method is utilized to studythe influence of doubly-fed induction generator (DFIG) onelectromechanical oscillations. On this basis, the smallsignal stability region (SSSR) of power systems with DFIGin injection space is evaluated and the corresponding relationship between SSSR boundary and electromechanicaloscillations is analyzed. The effects of the locations ofDFIG on SSSR are considered. It is found that the boundary of SSSR consists of several smooth surfaces,which can be approximated with hyper-planes in engineering application. With the integration of DFIG, SSSRbecomes smaller, thus indicating the deterioration of the small signal stability of the system. The 11-bus system with four generators is used to illustrate the proposed method.